My truck had a brake pull when I bought it which I put down to the drum brakes needing work. When I fitted the power disc brakes to my truck it still pulled slightly to the left like you describe.
On my truck it wasn't obvious what was causing the fault as everything felt tight when I got under the truck to check. I finally tracked the fault down by getting my girlfriend to drive the truck past me at walking pace as I stood alongside the truck and watched as she pressed the foot brake and came to a stop, the backwards movement under braking of the front roadwheels in the arches was obvious then, both of my spring pins/bushes were worn, but the pin on the lefthand side had 1/16" step worn in it allowing more backwards movement on that side and the resulting brake pull. Once I'd fitted new pins and bushes from Classic Parts, the brake pull was gone completely.
Stuart.
