We had a car fire last summer with a identical problem on a identical gtp. That was the biggest pain in the ass to put out since the guy was 300 feet off the driveway in a backyard.
I have a a t-5 out of a 91 that I ran in mine shifted great when I took it out and was tight in every gear. I'm going auto now so it's taking up space.
I have a brand new set of headman long tubes that have never even been flowed yet. $100 takes em. I bought them for my 88 1500 and got rid of it before I put them on.