Changed transmission, car moves when it hits 2000

Not likely a sensor most likely tork conveter lock up is not working or locked in or planetary gears bad. Valve body shifter solinoids could be stuck not sllowing to shift into high. so pull the pan and check to see if the pan has any particles in it if it does not then it is tork converter or possably you don't have the shift lingage adjusted right. you will have to shift it to park then adust the shift lever so that it is all the way in park, so try that first. if the fluid is brownish and smells like onions you may just need to replace the fluid and filter. If the transmisson you put in did not get a new filter then if it set for a long time the fliter could have jelled and plugged which could casue the same problem.