Unlikely it's the motors...any way to test one by applying 12v directly to the motor using a jumper? If one motor was good then I would assume they are all good and start with the module. Try Googling around, I found a place in Idaho called Module Masters when I needed the ABS unit for the Suburban, I got a rebuilt one for $250 instead of the $1200 the dealer wanted for a new one.
You might also see what other models this module was used on and see if you get one from a salvage yard.
I would be interested in the name of the company you found for the seat...I have a few rips on the drivers seat bottom and if I can get just that cushion recovered to match the OEM leather then I wont have to go to seat covers.