6L80e to 4L80e swap

I swapped my 2006 Sierra from a 4L60e to a 4L80e a few years ago and had hptuners do a segment swap and i added the wiring for the rear speed sensor etc so im familiar with the that swap. My truck has a cam, headers, intake, etc...
I have a good friend with a stock 2011 Silverado 5.3/6L80e and hes had the trans rebuilt twice in the past year by the same shop and it is toast again. He's already paid around $4700 and I'd rather him not give this guy another chance to screw it up again. Both times this shop rebuilt it the trans temps have been 210+ degrees and was supposedly rebuilt with performance parts. I havent seen a build sheet/parts list on what was put in it and they dont seem to really have documentation on what they did. I'd much rather do a 4L80e swap on it for now to get the truck back on the road and tear into the 6l80e myself over the next few months but i cant find a whole lot of info on the swap.
So here are my questions..Is the 6l80e to 4l80e swap similiar to the 4l60e to 4l80e swap when it comes to tuning? Can a segment swap be done or do we need a different tcm or even pcm? Ive seen the adapter harness for ~$700 but im trying to keep this very cost effective and if thats the only way then the swap is out of the question. The crossmember modification isnt an issue, welding/fab is my area of expertise, and the wiring isnt a problem either.
Has anyone here done this swap? I know its kinda going backwards from a 6speed to a 4speed but its hopefully just a temporary fix(year or two) til i can rebuild(trial & error) the 6speed.

Its an e38 with a T43. From what i've read i'll need a T42 tcm, correct?

It requires an adapter harness and new TCM. I make a plug and play setup for $600 that includes the TCM. There's no cheap way to do it.

The 6L80 / 6L90 have become my preferred transmission in custom vehicle / Hot Rod conversions. They can be tuned to hold up well behind some significant power - much more than your friends stock 5.3L can produce.

My experience has been that not all transmission shops can rebuild these well. There seems to be a tight tolerance in the allowable thickness of the clutch packs - which the TCM monitors (wear algorithm).

My two cents ... get a low mileage replacement 6L80 from your local wrecking yard. Make certain to flush the transmission cooler lines, and any in line cooler (radiator cooler, etc.). If your friend tows with his truck, an additional transmission cooler (plumbed after the OEM radiator cooler) is recommended.

Then tune for longevity - reduce the shift times and increase the shift pressure (gradually, until you find the shift feel that your friend likes). Trucks also have converter "slip" programmed in from the OEM - potentially to address "drone" during AFM operation. I always setup the converter tables like a Corvette - either the converter is locked or it is not (reducing the amount of torque converter slip also reduces heat).

A 4L80 swap can be great for very high performance vehicles, but the overall cost adds up quickly (to quite a lot).

Do you use a stock TCM from a earlier truck?