My son and I recently rebuilt the motor in a 98 neon sport. During first startups and checks it was on jackstands I put it in gear to make sure the wheels spun and everything was connected properly, hoses sensors, etc. seemed to be working fine. Now when the car is started it does not want to move, between 3-4000rpm it will move. Once it is moving it seems to come out of it and the transmission is working "properly" it just shifts with some slipping. Any help would be appreciated.