Thanks. I tried disconnecting and removing the calipers early on. Didn’t change. I also changed out the entire rear wheel assembly to go to a cassette system and replaced the brakes with hydraulic calipers. I don’t think that’s my problem. Also, it continues with light brake pressure on the rear brake.It's a bit of a stretch but you seem to have replaced and/or checked pretty much everything except the rear disc brake system. I convert most of my builds to disc's using homemade mounting brackets and have found ensuing the disc runs straight inside the caliper with minimal clearance for the brake pads is important. The caliper mounts usually have a small bit of adjustability, they are slotted to allow some alignment.
Appreciate your input.