1999 Plymouth Voyager Stalling

I just finished putting in a used transmission as the old one was shot. I got it completely put in and had the put in a new crankshaft positioning sensor and it started and ran fine. The first day I drove it to work(30 miles one way) and on the way there the transmission jumped like it was falling out and after a few seconds it was fine. It threw an error code so I checked it when I got back home, turned it off, got cleaned up then went to pick my kids up from school, shut the car off picked up kids then went to the bus stop to pick up my son and it dies. The error code was the camshaft positioning sensor and the parts stood said that would kill the car. I replaced the sensor it ran for about 8 miles and then died. Depending on how long u let it sit will determine how far it will go the next time. Where do I look for problems