my 1988 k5 came factory with 3.08 gears and a 465 trans -got along just fine on 31 inch tires, but man that was some tallllll gearing. Was like being in 1/2 overdrive all the time. cruised great at 55-65mph -almost like that's what the speed limit was and that's what the truck was designed to do??? even with the manual trans, the 3.08 was noticeably tall. I'm pretty sure that if I had kept those gears with the 33 inch tires, it would have felt like something was WRONG all the time. that could be worse with an auto?
If your truck has a code for the 3.08 gears, it probably came with a non overdrive transmission? i kinda scanned some pages here, but got confuse along the way - you have a th350? or have swapped for a 700r4??
fyi- im now running factory 3:73 gears between 35 inch rubbers. Given the 465 trans, I think its the best of both on/off-road I'm going to get (although I'm running a 241 transfer case for a little deeper low range gearing now). if your truck's previous owner did what I did? when a good ten bolt front is $FREE, and a rear end can be had almost free? its easier to go shopping for a set of axles with a higher gear from the factory, and roll the whole enchilada under there, than it is to buy parts and re-gear what you already have.
If i were running a trans with overdrive, I would want lower gears with the 35 inch tires on there now.