AF code is a 3.90 standard (non-limited slip) 1/2 ton truck rear end, Mark. 3.55 will only be a 9% improvement and that isn't a lot. Now that you have it sealed, I think I'd be inclined to drive it a couple of thousand miles to see how it does. Given what you've done, the only change ought to be that it doesn't leak now. I believe I'd do that before spending big $$ to change to a 3.55 gear set. Good luck!
