'97 Blazer LT, 4.3L, AWD, 4L60E with center console shift

Problem: no brake lights on left- or right-side only (center light works fine)

Additional: left- and right-side turn signals work. taillights work. hazard lights work. all fuses good AND specified amperage.
This is the 2nd time in 2 months with this same trouble. Problem appeared (both times) after my wife was using the vehicle to tow our pwc. (I've used it for the same purpose at least 20x more without incident).

First time it was the turn signal switch which I replaced with new from dealership. Now, the replacement appears to be defective. Are these switches prone to failure and what can be done to improve performance (other than not allowing wife to use vehicle for towing)?

TIA

Check the wiring harness going back to the brake lights.