Talk to certified in MI. It's the shop ZZP uses. If you want a good deal, register for MGM, and get the car towed there. Tell them you broke it (and as long as you're first) you'll get 1/2 off...LOL.
OK they prolly won't buy that.
Royal GTP had some Intense trans woes, and they had reffered him to a local place. IIRC Intense was a PITA, but the local place did a decent job. You may want to PM or e-mail him about his situation.
Our transmissions are hit/miss. Normally stockers can take you pretty far and last quite a long time. It seems that rebuilds are dicey. I know that you're looking for something bullet proof, but such an animal doesn't really exsist outside of GM Racing. If I were in your shoes, I would swap in a GT trans (better gearing) out of a lower mile used trans. You will need some of the parts off of your current transaxle to convert it to a HD model, but that's not too much trouble. There are also kits off the shelf to convert it over from Intense (GM parts).
If you can get it out yourself to do the swap, you may be able to do it easy for under a grand, and if you're really frugal under $500. I've seen low mile GT transmissions for $200. Contact Ed Morad to see what he has, he usually has a few transmissions laying around.