Installed a rear caliper, now all 4 are locked up!

[lowpost99]

I found a set on an 87' max from the junkyard. I installed them, and bleed the brakes, in this wheel order RR, RL, FR, last FL. We drove it and it sounded great, no dragging, scrubbing, good braking power, everything was good, and then about after about 5-8 minutes, the brakes began to grab hard(locked up is a better description) as the wheels began to smoke intensely (from the brakes pads I assume) so I drove home and parked it. Any idea what/why they could be locking up? When I drive, it feels like when the brakes are applied they work, but aren't releasing when I come off the pedal. The front brakes both were smoking and I've done nothing to either of them aside from bleed them. Any thoughts?

A special note, I had to replace the RR caliper because previously I pressed the brake pedal with the caliper de-installed and this stretched/tore the dust boot(I now realize my mistake). Both LR and RR were also pressed in with a c-clamp during pad install, (another no no). Anyway, this had me a bit worried about the LR caliper, as I did not replace it, so I thought I should mention it. Remember however, I can still hop in right now and all it's all good for about 5-8 minutes...makes me scratch my head...maybe I didn't bleed it right?