Easiest way to change wiper motor

Well I purchased a reman wiper motor from Advanc Auto(Cardone) and when I open the box it looks like a piece of crap. I remove the old motor, change over the gromets, ballast resister and spend the time to mount the motor to find out it is dead. I take the new motor out and remount my old one to make sure everything else is in working order.
So far I am getting juice from the switch to the wire leads that attach to the motor. The ballast resistor appears to be working properly as when the switch is on low speed there is less current running to the motor. When I put the switch on high the current becomes greater. I removed the switch and made sure it is grounded nicely against the metal dash. I have even added an extra ground strap from the motor to the fire wall.
Here is where it gets weird. My old motor will run in both low and high speeds when the linkage is not hooked up. It appears that as soon as the linkage is bolted to the motor the wipers will not move but the motor makes noise. When I disconnect the linkage and move it by hand there is no indication of binding anywere in the linkage. Everything moves freely.
I went back to Advance and they ordered me another motor. Could it be that although my motor seems to turn on and off it is not strong enough to move the linkage with load on it. Could something be stripped internally in the motor. The linkage all looks perfect.