Dave @ TEP is as good as it gets. Turbo 3800's break trans' fast if they are not done correctly. It will out cost almost anything else in your build.
The 4T65E-HPS4 package is pretty stout, but I think that still includes the 300m input shaft with the o-ring grove in it. If it does, I would ask to upgrade that too the no o-ring groove. They break at the groove. Also, the custom PI converter, get it in non-lockup and program that out in the ecm.
The GMR 1" chain is what you want, but the are running $3500-$4500 now-a-days. Good luck even finding one.
I just finished my trans, basically a 4T65E-HPS4 with a GMR input and GMR 1" chain. Going all out on this turbo build, so no expense spared. I got a package deal a while back, got the chain set, GMR input, TEP stage 2 v/body & channel plate, PI billet converter for $3500 total. Prices have soared since then. I have the tools & no-how to do my own, otherwise it would have been freighted back and forth.
I built my another trans built the same way, but has the 7/8" chain and the TEP no o-ring 300m shaft. I have not broken anything yet, while I am not sweating the TEP no o-ring shaft, the 7/8" chain will need to be changed as maintenance before it stretches too much.
I can not recommend TEP enough. You only need to have a local built trans fail one time, and it likely will with a turbo's 3800...to realize you wasted a bunch of money not paying for shipping to get it done right at TEP.