1995 chevy s-10 blazer wiper motor park problems

Replaced wiper motor with used one. Wipers have full range of motion (all the way up & down), where they should be. My problem is where the windshield wipers park. They park about 1/4 to 1/2 the range of motion in the middle of my line of sight. Is there something that i could have done wrong to cause this or is this a used wiper motor or transmission problem?! I took the nut off of the wiper motor to put on the new one could it just be that i have the transmission a couple splines off or something totally different?! Please R.S.V.P.