1995 E350 Shuttle Bus brake drag even after new brakes

I have a 1995 Ford E350 shuttle bus manufactured by the now-defunct Metrotrans. The parking brake light and ABS light are always on and the rear brakes intermittently drag, causing them to heat up excessively and damage themselves. I had my mechanic completely replace everything in the rear brakes including new drums, as well as replace the parking brake hardware and rear ABS sensor and adjust the parking brake cables, but the brakes still drag intermittently. Me and the mechanic are scratching our head as to why this is happening. Has anyone else experienced this or knows what might be the issue?

• This topic was modified 2 years, 5 months ago by . Reason: Additional details