a sebring interior for my 66 dart

Sounds like you have a good plan in place. I know the up/down motor in my 04 Sebring isn't the speediest so what you have may be normal.
I just called a yard near me and they have a 97 sebring. I'll be going over there on monday to grab the rear seat metal for mounting the rear seat and I'll grab a motor or two to replace the slow one since they all look the same on mounting bolt locations and the wire color code looks to be the same too.