transmission has about 150 runs total, had no indication anything was not kosher, fluid not burnt or discolored. first round of eliminations, rolled the beams when I put it on the 2-step. been building my own transmissions for a long time and never saw anything like this. the rest of the transmission looks perfect. griner LBA transbrake if it matters.

That band is only applied in reverse unless you have a low band apply valve body. Even if it was low band apply it's only helping hold the drum along with the low roller clutch. Therefor it should slip. Did you check the adjustment before disassembly? Possibly to tight. It looks to me like it's been dragging in other gears. Is it a stock servo? Does the servo piston show any signs of being cocked in the bore? I suppose there could be an internal bleed in the valve body. To late now but you could check for pressure at the rear servo in N, 3rd, 2nd. It should read 0 in those selections. If it's non low band apply it should read 0 in 1st as well. any pressure in those selection would show a cross feed.
Doug

Misalignment, cocked band maybe

Slow servo release. I'm assuming you have stock pieces in the reverse servo.


Hutch

While I agree with the possibility of band too tight , or a cross feed ... why would that only cause half of the band to drag/burn ? I looked for any chance the band was mis-aligned or crooked, but it all looked as normal as can be.

Look at the way the drum is constructed. The area of band contact where it looks good is at the thick portion of the drum. That area is a better heat sink for heat dissipation. The burned area is thinner.
Doug

Good point ...i had to go back and take a look.

My guess is the low servo piston cocking in the bore and sticking, then being just stuck mechanically the band not hydraulically applied it will drag and the band can slide back and burn one side. The rolling when going on the 2step I believe is a different problem.

Another remote possibility, cross-leakage of fluid pressure from the accumulator to the rear servo. Lay a straight edge on the case where the accumulator and the front/rear servo ports are to be sure there is no irregularity in the surface to allow cross flow. Ditto for the VB in that area.