I have a 1999 with power locks and the drivers side will not lock with the button or key fob but the passenger side will.

 

Fault in the wiring or a bad lock selenoid.

 

it try's to lock it just don't go all the way down and the more you hit the button the weaker it gets

 

Reads like an issue with Drivers door switch or relay, since passenger door button works all the time to Lock door

The Drivers door switch AND the FOB both used drivers door relay, passenger door switch doesn't

I would locate and try a new switch first, or swap switches around they are the same

There are 3 relays for the door locks
All unlock
All lock
Drivers door unlock/lock

Drivers door switch and FOB both use the drivers door relay
Passenger door switch does not, its wired directly to the all unlock and all lock relays, so these two relays are working and the driver's door "motor" is working

These relays are in Relay Box 1, above gas pedal in the cab, it has several relays inside depending on your options, there is a removable cover over it