American Powertrain offers an upgrade option for the TKX ... says it can handle 900 lb.ft. See: https://americanpowertrain.com/shop/transmissions/tkx-5-speed/tremec-tkx-extreme-upgrade/

I was on their website several months ago and they mentioned that they were working with Pfitzner Gear on an upgrade gearset for the TKX. I don't see that mentioned for the TKX anymore but they do mention this gear upgrade for the Magnum 6-speed at: https://americanpowertrain.com/amer...ear-upgrades-for-tremec-magnum-6-speeds/

I'm in the same situation needing an upgrade for my A-833 ... I've come to the conclusion as AndyF says that a race automatic with a transbrake is in my future. I've been rowing my own gears in the Cuda for 40+ years but its time for an automatic now. It will be tough to look in the console and not see the pistol-grip shifter handle in there.