Suburban seat problems

sounds like the motor brushes are about worn out.
Where you actually sitting on the seat when you applied power directly to the motor? If the motor is wearing out, it may work under little or no load but won't work when your weight is on the seat. Will the seat move while hitting the button if you also help push the seat in the direction you are trying to move it? If yes, the motor is weak. Change the motor, check, clean and lube the tracks, if nec., then see if that's better.