When using park brake the truck still moves. Is there an adjustment for this?

 

Sounds like you need to bleed your rear brakes. might be air in the line.

 

So there is no mechanical adjustment?If so am I in need of new brake pads?

 

you can tighten the cable under driver's side or adjust the pads. they are drum brakes internal to your rear rotors. you should use a brake adjusting tool as getting to the star adjuster is a pain without removing the tire and rotor. If you have adjusted drum brakes before same thing. You may want to check to see if the pads are still good though first.