For the TH400 trans we use ATI, they are reasonable and reliable.Choose your converter wisely. Just for info purposes, if you call ATI for a turbo Buick converter, they call me to spec it out anyway.If you know someone with a combo similar to yours with an ATI conv, call them with the serial # and they can duplicate it exactly,you can choose to buy direct from them but generally it will cost 20% more,usually happens about once a month for whatever reason.We are a WD for ATI restalls are free for 30 days,(longer if I screw up!).