Lol truck really has no rust so im hoping it wont be too bad.
Say I go with 4inch lift, to fit something bigger thn 35s people say I need to trim, is that the inner fender, or the actual body panels of the truck?
If I wanted to go up to say 37s just for the hell of it.
Most likely only the outer body panel. Run your hand along the upper inside of the wheelwell; there's a lip there of the body sheetmetal for a few inches before you get to the inner wheel well.
And at 37"s you really oughta think about D60/14bFF if you haven't already.
And I see alot of tires seem to be the same size but look diffrent, is that based on the width of the rim or something? And how does that work?
Tire sizes are approximate at best. Yes, the rim width affects the actual diameter. most manufacturers list the inflated diameter of their tires on a specific rim width, and they also should list an acceptable range of rim widths.
Is there a marking somewhere in my truck that I can find out what gearing I have in her? Looking to not change the rears(axles?) never sure what they were both called when refering to the whole piece. But if have to,I dont have the money to go one ton and I prob wont wheel this thing that hard to need them in a long time.
"Axle" is best, inasmuch as calling anything on the front of the truck a rear end is a bit silly. (The term "rear" comes from cars which have only gears in the rear axle, being 2WD
)
You may have a sheet with the options ("RPO"'s) in the glove box. The only way to be absolutely sure is to pull the covers and count teeth, but you can prolly turn the wheels and count revolutions.
So as far as 3/4 tons, is there something that they came in that would bolt right in to my 91k5 and will have a better gearing for me? 4.?? id assume.
Thanks alot everyone
With numerically lower gears, like, say, 2.73:1, you end up with a lower crawl ratio and no torque off the line, but you get lower engine RPM at highway speed. (With larger tires, you also risk killing the tranny due to excessive torque required to spin the things.)
Numerically higher gears (e.g. 4.56:1) give you stupid grunt off the line, but wind your engine up faster at speed. You also get better crawl ratio, i.e. more throttle control at low speed and in low gear on the transfer case for better control on the trail.
Gearing is decided by what RPM you want your engine to be spinning at a given speed, and is a function of your transmission's highest gear as well.
There are lots of gear calculators online; Google for it. Note that your '91 should have a 700R4 tranny, which has a 0.7:1 overdrive (the older auto trannies have a 1:1 "high" gear, i.e. third.)
Jeebus, that wasn't supposed to be so complicated =))
Also note you'll want to look into speedo correction. Your truck may have the DRAC, an electronic thing, which makes it more complicated than changing plastic gears in the tranny. I think.
EDIT: And to actually answer your question ... yes, lots of 73-91 3/4 ton trucks had 4.10:1's from the factory. Swap in a set of axles off such a truck (pickup or Burb) and you're golden. They'll bolt right up, and if your donor truck is of matching years, even the parking brakes will cable up properly.
-- A
, and be prepared to have to cut some bolts, mainly the bolts going through the leaf spring bushings, so get some new ones ahead of time. I have yet to have all of them come out on any of the approx. 15 of these trucks I have lifted or just torn apart. That is all I can think of, I am sure others will add some more stuff for you to think about.
for room for bigger tires 
