2008 gmc 2500 passenger caliper sticking
 

Would really appreciate some advice, I'm helping my uncle with his 2008 gmc 2500. He replaced the front roters and calipers and the pasenger side is sticking he did bleed it but still sticks. This is where i came in.. we take the caliper back and excange it for another new one, put it in and bled all calipers and it's still sticking.
Thanks