Everybody here talks about the p30 Chevy chassis but yours should be a Workhorse chassis as chevy in their wisdom sold out to them. Along with the problems, but I haven't run across where there was a recall when there should have been a recall, on the auto brake and the caliper system brakes.
Chevy took the simple hand brake and replaced with electro-mechanical high tech(POS), instead of modifying the transmission by adding a sturdier prawn to hold in park. The caliper brakes on mine suffered from overheat in rear due to crud in the fluid, water boils off and steam doesn't compress the same as brake fluid, but my feeling is that the slide mechanism on the calipers gets rusty and freezes up. When your mechanic replaced the calipers and turned the rotors, did he do a through job of cleaning up and testing their release as well as their application? I found an IR thermometer can aim and check exactly where the hottest spot is around the wheel and axle.