Seems like this should be easy to diagnose. When they are acting up jack a wheel off the ground and open the bleeder. If it frees up then its a hydraulic issue. If it still drags after opening the bleeder its a mechanical issue. This needs to be done to continue diagnostics.
Just did this this morning. Cracked the bleeders and fluid dripped out. No pressure. The calipers were both loose. Last night I couldn’t turn the tires because they were so tight. Over night, no drag at all.
You have to do this when the brakes are dragging. Even waiting 15 minutes gives you false information. The problem can go away that fast. If its a reoccurring heat issue, you have to open the bleeder screw while its hot and still dragging to see if there is still pressure there.
Get them hot and dragging, pull into the unoccupied end of a parking lot, stop and open a bleeder screw (caution, the fluid will be hot). If it squirts out and the wheel turns, there was still pressure applied.
