I bought my pickup it has 31toyo tires on it I can go 75 with the overdrive off on flat land down hill it will go way faster in over drive I'm looking to change the gears but I'm not sure what they should be to still handle high way speeds

 

Just what are you looking for in the end here ??

A top end speed of 120mph even though it might take 5 miles or so to get there.Falling off real fast at even the idea of a slight incline.

In your case about the only thing is a engine upgrade

The automatic 22r Series engines are not known for being quick off the line

At slightly over a 100 horsepower in a heavy 4x4 truck put the same engine in a much lighter Celica with a 5 speed a fun car to drive.

You can find the effect of different gears with your tires see if it gives you what your looking for

 

If you haven't, tune up the engine and clean the intake plenum/ throttle body. The 22re is no power house, it's just easy to work on and tough. With A/T id guess you have 4.56 in the diffs. 4.88 would be the next step but that's real pricey and it isn't a big jump.

 

What gears do you have now? Have you checked the door codes?