How do I get brake piston to depress to change brake pads?

Tried the other side still not budging even opened the bleeder a little bit.

Wrong tool being used OR wrong technique. Get someone to help you out here! If both calipers were stuck that bad either the pads were worn completely out and so were the rotors or the truck would not have moved as the brakes were locked up and the calipers would have to been pried off with a pry bar. Tell the whole story!

It is the whole story, but it could possibly be wrong tools. I used squeeze c-clamps the kind with the trigger might not be getting enough force, but I also tried a large pair of channel locks no budge. I'm going tomorrow to get a set of screw tight c-clamps see if they will do better. The pads were very warn. To the squealers but still some life not much though. Rotors are fine actually and calipers came off relatively easily.

Ok, sounds like you just need a bigger/better clamp. They dont just ease back, it takes a bit of force! Search youtube for the video on the correct tools and procedure! In fact it's one there for a truck just like your's. Check it out before you buy any tools, you'll see what size clamp is needed! The procedure is about the same all front disc pad replacement. ★Important note; when finished with the install, pump brake pedal about 10 times before starting the engine!!!