when i turn it on...it stuggles to operate....but when i get out of the car and lift it a bit with my finger...it works perfectly fine....is it because its too tight and its pushing itself to much onto the back windshiel?....

 

check the springs on the arm it self.

 

it could just be old and tired, I've seen lots of wipers run slow when the windows are dry from the extra drag.

 

try using it when its raining, just let it work in. i used to get that with front wipers. after some time it starts picking up, the rubber softens up a bit and motor works in.
but yeah its time to replace the motor.

 

how much is the motor?

 

i just did a wiper delete, could sell you the motor if you want