I think my driver door electric lock motor is going bad. The door will unlock but will not lock with the button. The key will lock it though. Any advice on replacing the motor in the door?

 

Mine does just the opposite!.. lol
As long as the solenoid it operating, you should just need to clean and lube the mechanism inside the door.

 

*Moved to 2nd Gen Tech* - made an assumption about what you are driving. Please let us know the year at the very least.

I agree. If the solenoid is making an attempt, the latch is likely just sticky and needs to be lubricated and worked. The lock solenoid may be part of the door latch itself, but that depends on the year of your truck.