My 04 Colorado has been doing that since day one. I've chalked it up to the float going down when the gas moves away. Never caused me any pain other than an occasional low fuel warning that clears when the gas settles down in the tank and I start moving again.
Well I just did a little searching with Google. Found a post that makes the most sense to me.
"It's common for several sensors to share a 5v reference circuit, its likely one of the sensors on the transmission shares a 5v power supply with the fuel sensor. When one sensor suddenly draws a lot of power the others will be skewed."
I'm going to be cleaning some grounds the same time I replace the harness for the blower motor resistor. Ill see if that helps any towards this issue.
I'm not really worried about it. It has done it the whole time Ive had it. Just curious