Little late on this thread, but it sounds like the cheap fix I found could be helpful. When the motor seems weak it's often just the plastic gear busted to pieces. If you remove the screws from the circular part of the motor housing and clean out the pieces, you can put a ball bearing or nut on each side of the triangle and get solid purchase again. Worked for me and I returned the motor I had bought to O'Reilly.

 

I put three nuts in to replace the old plastic spacers. Works like a charm but watch your fingers.

 

I ended up replacing the whole thing, too cold to mess with it
I saved the box, receipt etc
If it fails again it goes back & they give me a new one for free
Dang thing always seems to fail when it starts getting cold
I've actually been using the drivers window LESS since it failed the 1st time
There is no way these things should fail like this

I tested it before I put is all together
Checked the door locks too.....drivers side door would not stay locked
Then I realized I had started the truck, so a safety feature so you don't lock the keys in

I measured the speaker while I had it out....6x8 ?
I guess I'm just used to 6x9's.....
I've been looking at the Polk Audio DB571...but they are 5x7's
I guess if they fit & sound better then stock........