Welcome to the 'bolt, ChevyGirl. I agree with the above comments; swap the tranny first and see if it needs the rear gears changed, I'd bet it doesn't. 3.55 is not a huge jump from 3.90, it may do more harm (1st) than good (5th). It will definately need brake and suspension work to safely pull it back down from 75+ mph.
Are we going to see this truck in the gallery?
