Should I change gear ratio?

[Botlfed]

Im just goin off of what my gears top out at and its the same with txakitekt, he also has 4:10s. mine is programmed to 130 but i never get there.

[LS1GMCTruck]

How much does an in inch of tire diameter change the final drive ratio, or rear end gearing?

[RedHeartbeat]

It depends on what gearing or tire size you started with.

28" tire has a rollout distance of 87.96"
29" tire has a rollout distance of 91.11"

you travel 3.15" further down the road per tire revolution if you travel at the same RPM/MPH. In 1:1 lockup such as 3rd gear in a 4L60e that's an increase of 3.6% distance traveled. On the flip side you reduce your engine RPM by about the same 4% if you maintained the same RPM from the 28" to 29" tire.

[derf]

How much does an in inch of tire diameter change the final drive ratio, or rear end gearing?

I know this is an old topic but I wrote a Java applet that lets you plug in all your information (tranny, t-case if you have one, gear ratio and tire size) and it will show you a pretty close approximation of what RPMs you'll run at different speeds in all the gears as well as what speed you'll be going at certain RPMs in all gears. There's two copies of the form so you can do a side-by-side comparison.

Gear Ratio Calculator

If you're running a 2wd truck, just pick (almost) any transfer case and ignore the stuff about low range and crawl speeds.