my controller stopped working.its the one chevy sells. i cant remmeber the name of it. so i had a friend thats really good with wiring and stuff take a look at it. i was getting power all the way to the trailer but the brakes werent working. checked the fuse and all the connections and everything was great.i thought maybe a bad or loose ground.but if it had power going to the trailer doesnt that rule that out? we loaded the trailer (small load 5900lbs total) and went to get fuel just to see if they would start working and sure enough all of a sudden the brakes started working immediately after i fueled up and have worked great ever since 500 miles towing later.

95% chance it is a wiring problem on the trailer. I see a lot of bad wiring on trailers.

To the best of my knowledge GM doesn't sell brake controllers. You dealer probably carries this brand.