C32izm

My 2003 c32 that i recently picked up is giving me too many headaches, when i got the car the tranny had too much fluid in it, drove it for little, tranny seal popped. the tranny had a jerk in it prior to the seal popping so i just decided to swap the whole tranny unit. put new fluid, filters, seals, rebuilt torque converter, rebuilt oil pump. got it back from the mechanic the car was still jerking between gears 1-2 and 2-3 and also down shifting. when i put the car into gear it bangs really hard and you can see the car jerk from the outside. put it in winter mode while i was driving one day to see if it would still jerk while shifting. while it was in winter mode it was driving like a dream, came home, parked it up, wanted to go out in the night. backed it out the drive way the transmission was completely dead it wouldn't even engage or anything just completely slipping. i'm not sure if something went wrong during the install or if the whole unit is a failure I'm not sure i just need some advice and a recommended reliable shop in the NY area,