I'd be inclined to change the gearing if you have the money. It'll probably be gutless off the line if you don't, and gas mileage will go down. What size tires now? What gearing do you have now? Take a pic of the tag on the door or door post and post it up, or look at the metal tag on the rear end.
The metal tag is no longer there and the inside door sticker says that the axle is 84. Does that help? I'm not using the truck for anything besides commuting. I'm not looking to blow anybody off the line. Just for a better look than the stock.
Assuming a 195/70r14 with 3.45 gears ~= 31" with 4.30 gears which they don't make. Nearest commonly found is 4.10
~= 33" with 4.56 gears
If I was paying someone anyway I'd go with the 4.56. Doing myself it's not to hard to find 4.10 geared axle and swap the whole axle.
It may place a small strain on your transmission if you don't regear, but I think you should be okay since you arent going with that much larger of a tire.
My truck originally had 3.73 gears and ~30" tires from factory. I lifted mine and ran the 3.73's with 37" tires for about six months and the transmission crapped out on me. Then I switched to 5.13 gears and the truck rode MUCH better.
I agree with Richard, regear if you have the money and want a better quality ride, but IMO, I dont think you will hurt anything by running your current gears.
Buying a completely new rear axle will probably be your best bet as they can be found for cheap in junkyards. Just make sure you check the door tag. 3.73's are fairly common and 4.10's are a little rarer.
With 215/70r14 and 3.45 gears ~= 31" with 4.10 gears, would be as good as you could get, the speedo is correct.
~=33" with 4.56 gears, pretty good, the speedo is 5% off
I think Danny is correct, with an auto, make sure to have an auxiliary cooler. With stick, don't ride the clutch.
I bought a set of d-28 axles for my b-II that were supposed to be 4.10 for C$200.00. The front are 4.10, the rear are 3.73. I don't use 4x4 except in the snow! In 2wd, it's a little bit of a pain taking off, but I've gotten used to it. I have 31"/10.50r15 and a stick.
I've got another 4.10 axle, just have to go through it and install.
fear and common sense is the only thing stopping us from any mod i say just do it , and see how bad it is . re gearing can always be preformed down the rode .31s and 345s i ran this for a bit and found.. speedo will be out , kiss that last gear good by ,if its a 5 speed. passing semi trucks should be done with great care. if theres a 50 mph head wind , you'll want to find a diff way be sides the freeway. that hot smell all the time is your clutch begging for mercy. i would trip a round the jy and find some 410s . 373s on 31s with a warmed up v8 works well.. >:?