1500 Pads and 2500 caliper

[454cid]

No idea on the play, but it sounds like your brakes aren't quite right... the calipers are new, right? So the rubber around the pins should be good. I think you mentioned new pins, too. How about hoses? Those can deteriorate inside and act like a check valve... and it sounds like your brakes are dragging a bit, to me. The other thing would be the pads not being for those calipers... check for weird wear, maybe?

Do the matching pads for the caliper not fit the 1500 rotors? I don't have a 1/2 ton, so I've never looked into this swap in detail.

 

[JackE]

Swap your front tires, see if the pull goes away, or moves to the other side. Radial pull can appear out of nowhere.