32's will be a lot better for mileage/economy than 33's will be.
I drive a Z85 with 31.7' and my mileage is barely 15 mixed driving. 20-21 highway if I drive easily.
The shift points are pretty screwed up, OD has no torque when on the low end, like 40-60mph. With 33's, it will be worse yet.
I think my tires are 9.6% larger than stock. That means the speedometer is off by 9.6% at all speeds too. 33's of course are even more inaccurate on a Z85 computer.
Greg makes great points about the torsion bar cranking. I think that is too extreme.
When you lift your truck.....with the truck parked on level ground, measure the distance from the center of your front hub vertically to the bottom of the fender lip. Stop at a 24.5 measurement. My Z85 only let met go to just over 24". I'm not at 24" or a little less. I've flipped my ball joint and added a spacer. That allowed me enough clearance to hit 24" without doing damage. But the ride is pretty bad. I can't hold a straight line on rough roads, and hitting a rough patch in a curve is pretty scary since I end up skipping in the direction of the body roll.