The stock carriers is my 88YJ couldn't even work with 3.73.
For a Dana 30, 3.73 was when I needed a new carrier. Anything lower could utilize the stock carrier.
For a Dana 35, 3.55 was when I needed a new carrier. Anything lower could utilize the stock carrier.
This is kind of a bummer because even 3.73s are a tolerable ratio (with oversized tires) if you're on a budget and don't have a few hundred $ to spend on carriers.
So if I were to swap the 4cyl.'s gears into my 6 cyl's axles, would I experience a rise in my acceleration and gas mileage with 33" tires? Is it nesessary that I but install and overhaul kits when I find the gears?
Yes, some of your lost accelerating power would be restored. Gas mileage is another question. I put 3.73 gears in my axles with a Chevy 350 engine. About two months later is swapped up to 4.10 gears. My mileage didn't change a bit.
I'm confused about what you mean in your 2nd question. If you're asking if you should install overhaul kits with the new r&p sets, the answer is definitely yes. You can get installation kits which include everything needed for an install at Randy's Ring and Pinion Svc in Everett, WA. They are SUPER helpful toward the new guy when doing install work. Their number is in the back of almost all 4wd magazine.
Just an idea but if you can find a complete axle assembly from a four-cylinder, why not swap the whole thing in and forget about all of the setup expense. Of course, this assumes that you find one with low mileage.