Regardless if the tranny is a C6, or AOD, a new engine, especially a very built one will take its toll on the clutch packs in a tranny that has miles on it. Gack, you should consider going ahead and have the tranny upgraded with alto red clutch packs and a 300m center shaft. Maybe even a wide ration gear set. The other option would be the 4R70W and Baumann controller. Hell, you already have your left nut in this project, may as well through in the right nut too.