Might have been better off saving the extra $20k for the SLP bits and bought a factory stock G8 GT and kept it stock. That would have been the only way out of this "on GM's dime".
I know what you're hearing isn't what you wanted to hear, and most of us here see your situation and feel somewhat bad for you, but to be honest with you, if my "bolt ons" car with 55k miles that makes 351rwhp had a supercharger and smaller pully, I'd be almost certain that the extra strain on driveline components would have caused FASTER wear on my transmission and drivetrain components. But then and again, I don't have a supercharger, and I'm getting by with my stock stuff no problem.
It all comes down to you purchased a car that you didn't adequately understand as it pertained to warrantees. "Get it in writing" applies here. When I bought my G8 GT factory fresh, I had (and still have) the warrantee paperwork of what exactly is covered under powertrain, what might void powertrain, and how to properly file a claim. I also have headers, HFC's, SOLO catback, aftermarket intake, etc. Am I filing warrantee claims with GM? Nope. If something breaks, I will be putting my money into fortifying the part that broke and ensuring that the car is better/faster after the fix.
Sounds like you're just looking to get out of it, which is somewhat hard to swallow since it doesn't currently run.
Get a quote for how much GM estimates it would take to fix the tranny. Then compare to Circle D and other transmission speed shops. Find out if cleveland pick-a-part or similar junkyard might have a good condition lower mileage 6L80e transmission that you could buy, and research the TCM VIN matching process on the replacement transmission, ensure that it will be doable. There are many options, no, none of them "free" as it were, but at least you have options.
See what it will take to fix the tranny straight up as a baseline (so you could sell the car in working condition) to recoup your investment then buy something else.
Does not seem like your heart is in it anymore, sounds like you just want out.
I can think of maybe 2-3 people who would love to get their hands on a Firehawk "shell" and get to work installing a fortified transmission, and fixing some of the stuff that SLP didn't do so well on it (drone master!) to take it to the next level.
Are you sure you have exhausted all options with SLP directly? If you get a quote from your GM dealership to PAY THEM to fix the transmission (irregardless of warrantee situation) then could you submit that in good faith to SLP and discuss? I've seen companies worth their salt step up and offer to reimburse for half or sometimes more... but you need to press them in an objective and positive way. No way SLP built a car that would only last 44k miles... and if you can convince them that if they were to try and work with you to resolve to get your car back into working condition, then you'd be a happy customer once again, that might be a win-win for all parties involved.
This was never a GM powertrain warrantee issue, and I'm glad it seems that you finally realize that now.
Maybe SLP will stand behind their work or possibly help out if you invite them to. Can't hurt to ask.
But if you're looking to get out of the mess you're in now, good luck to you sir on selling the broken hawk.
for what it's worth, trying to help