6l90e keep or swap?

[rustyrodknocker]

Hello ls swappers. I'm getting ready to swap an 08 6 liter and 6l90e inty o my 66 suburban. The donor truck has no reverse. I have learned that this is very common with this era of trans. Likely a failed clutch shell.
Something I'm struggling with is the cost of rebuilding is nuts.
Used units are likely to have the same issue. Also all sources I've reached out to have recommended swapping in the old internal ecu to avoid communication issues. With any option likely needing dealer programming.

So this bears the question. Am I better off to swap to a 4l80e? Or does the wiring harness work that comes with that option equal the brain damage associated with the 6l90e?

I will appreciate any feedback. I've been stuck on this for months. It is an issue that money will clearly fix. But the cost is just more than I can justify, to put a used motor in an old truck. I recieved an estimate today for all parts required to convert one of my big block mopars from auto to built t56 and its less money than rebuilding a chevy transmission!