Factory Trailer Brake Controller (ITBC)

[Phantom 4D]

2019 Sierra SLT X31. Recently towed our 20' enclosed trailer on a 2500 mile round trip. About 500 miles in I started getting "check trailer wiring" "Trailer Brakes Connected" on the DIC. When the check wiring came on, the light on the controller would go out. I noticed this would happen in gradual left/right curves and backing up. In heavy rain, it was constant. On straight roads it was ok. A complete check of trailer wiring was done and no faults noted. I've been told this may be a problem in the ITBC module. Any help would be appreciated.