sorry if this is a repost... I tried a search first guys... I have a 90 gmc 4x4 350/4-speed auto/3.55 gears. I currently pull a small 1700 pound trailer but, I am looking at a 6000 pound 23ft trailer. I feel I need to regear.. I was wondering if you would go with 3.73 or 4.10's. I really need to find what the towing rating is for these trucks with these gears. I run 265 tires and it only has 35k miles and it really good shape so I think the truck can take it. I already added a tranny cooler so what do you guys think?

Ok, to my knowledge, they never came with 3.55's from teh factory, i think it was 3.42's, 3.73's, or 4.10's (but i could be wrong). My truck came stock with 265 /75 16's and has 3.73's. The general rule of thumb is that it isn't worht the cost to go 1 step in gear ratios, and 3.55's or 3.42's to 3.73's would be one step. The performance difference isn't really worth the cost. Remember you've got a 4x4, so you have to regear front/rear.
If i was at home i'd look up your factory tow rating, i think i have a 90 sales book, but i'm at college rite now. What cab/bed combo is it? 6000lbs is probably within the max rating, but its a lot of weight. If you are paying to have the gears installed, you should look into what a 90 or older 3/4 or 1ton truck would cost you, you may find that its not worth regearing. Anyways, got a bunch of my opinions/ideas in there, hope it helps!

I have to agree. I run 4.10 and used to have 3.42 and I've been real pleased. Jump up 2 gears and reprogram. You'll probably like it a lot better and have more torque.

it doesnt matter what it came with cause whatever it is , is to high geard, id go 4.10s

Keep in mind future plans for a lift and/or larger tires