As with most things, there are pros and cons to both methods. Before deciding it would probably be a good idea to check the condition of components.

if you were going to drop the tank, are the fasteners corroded? Will the straps need to be replaced? Will you need new parts for the fill tube?

Raising the bed? Are the fasteners heavily corroded. Do you have a suitable jack to assist with raising the bed? A Reg Cab will obviously have a larger bed.

If you would be dropping the tank you would need a suitable support for it, even if it was near empty, especially if doing it alone. When installing it you would need something to hold it up while you connected the fuel lines and connectors.

My preference would be to raise the bed. I have done several full size ones by myself. It just requires some planning. I just remove all the fasteners on the left side and loosen the right side and make sure the wiring and the bed will clear at the aft end. Remove the fasteners holding the fill tube to the bed. The positive aspect is that you can do all the work and then accomplish an operational and leak check while you still have full access.

Obviously you would need to apply all necessary precautions to insure the bed does not return to the normal position while parts of your body are still under it.

Unless you consider it a fun job that you wouldn't mind repeating, I would suggest OEM parts.

 

I have done both with a S-10 and a Silverado, and didn't like either. A guy I used to work with found a better way - He cut out a "Door" in the floor of the bed right over the fuel pump, and put a couple of hinges on it and laid a bed mat over it. He knew He was going to keep the truck, and about 6 or 7 years later, the fuel pump went out. I remember Him looking us up at work soon afterword, saying "Do it! Man, just do it! You wont be sorry!".

 

I have an extended cab 08 and I'm for removing the bed completely. No method on an older truck like mine from N. E. Ohio would have been easy, especially when doing it yourself. I built a scaffold type device that slid under the bed and then jacked up each side a little bit one at a time then pulled the truck forward enough to clear the pump assembly area. The challenging parts were the two of the six bolts closest to the cab. They started to spin and I had to cut the mounting area to hold the captive nut to prevent it from turning. Next problem was the quick disconnects on the fuel and vapor lines. Those guys are super hard to come apart given the amount of dirt that jams the fitting, I ended up breaking two of them and had to buy costly replacements. The lock ring was no easy task either, I ended up buying an impact ring removal tool to use and it still took more than a day and a lot of penetrant to free it.
The bottom line, I never could have worked on the lines or the ring with the tank dropped. There just wouldn't have been room for the leverage and tools I used unless the space above the tank was fully open, remember also the pump assembly is quite tall and needs to go straight down into the tank. Another advantage of removing the bed is once I got the pump out I was able to remove the fuel, it was completely full, then I did drop the tank to replace the questionable tank straps. If your truck has a lot of rust now is a good time to replace the fuel filler neck. This job isn't easy and yours may be harder or it may not, but make a plan before just jumping into it and it will get done. Good luck.

 

Do you have a crew cab? I have a crew cab and tried doing the bed raise and it's impossible because the pump is half way under the crew cab portion.

 

That leaves you no choice other than dropping the tank. Not a great scenario without a lift, especially if the tank has a lot of gas in it.

 

Hey, I am not joking about the "Door". The guy told me He got under the truck and looked to find where He could cut the square hole in the bed. He took a short piece of rebar with one end ground down to a point, then found where He wanted a "Corner" to the 10" X 10" or so square hole to be, and with a hammer blow to the rebar He dimpled it so He could find where to start work from above. From that point of reference He used an angle grinder to cut out the "Door", 2 hinges on one side and a flap stop on the other, and covered it all with a rubber bed mat to haul stuff in the truck bed as usual. When His fuel pump went out, replacement was a breeze.
When your fuel pump goes out in these trucks, I chit you not, THAT is the third option!

 

If it's a crew cab that won't work, the pump is under the cab.

 

Looking at the OPs pic there, looks like a Reg cab. I am on team OldTime here. On my 08 Ext, I lifted the bed. I have a small electric winch wired up in the rafters of my garage that I used. I had to cut 2 of the bed mounting bolts due to broken loose nuts.
The locking ring was a pain in the butt, due to corrosion. The proper tools would have made it better. I ended up cutting that off too. Just get a new one while you are at it, most likely not worth saving. Also had a heck of a fight with the fuel line connectors, even with the proper tools for that.
I took Cart's advice and purchased an OEM pump. Aftermarket pumps have been hit or miss in my experience.
Being able to fully test the system while you still have access is a great advantage.
I dont dislike the idea of making the access door. If you go that route, have the new pump in hand so you know exactly what you have to get through the hole, and size the hole accordingly. If the truck is a southern vehicle than maybe, but with the rust wrestling that I had to do, the access hole would not have been sufficient.

 

Side story here. A friend of mine spent 19 years working for a couple of GM dealers. If there is a short cut rrick he knows it. He hired in as a mechanic for a local electric utility company. His first job on the first day was to replace an in tank pump in a company car. About 1/2 hour into the job his new boss came by and said "What are you doing? That car belongs to us. Cut a hole in the trunk floor and replace it that way. When that car is retired from here it is going to the junk yard." About an hour later he was done and went to look for what was next. The boss said that pump job is your assignment for the day.

He is no longer doing that job. He now is a Power Plant operator with the same company.

I have never replaced a Colorado pump Around here we have done many Blazer pumps. They last about 100K miles and 2 of the our Blazers have over 250 K miles. My daughter replaced the last pump in just over 1 hour by dropping the tank. I have done one Ford Ranger by removing the bed. In my opinion it sure makes the job easier that way. My GM friend use to lift the body on Blazers (6 bolts, a shift linkage, and one electrical cable). He can replace the pump in under an hour. He got paid by the job and it was billed by the book at 4.? hours.

I have zero experience on Colorados. I only own one and it has over 150 k miles on the original pump.

 

Thank you for all the input - Answering question, I dropped the tank - {[Struggle bus]} Wound up having to pull the transfer case as well as the exhuast due to a plugged Catalytic (Aft) When was all done this poor little truck has a new engine, new front brake rotors (Chore) along with ABS sensor rings, Fuel pump and lock ring, fuel pressure regulator - a "Cleared" rear cat FINALLY it runs like it used to -- Just in time as the "Combat Horse" (GMC Envoy XL) literally blew the right front wheel brg out as I was driving. I just seem to have a thing for this Atlas engine family