Chevy intergrated brake

I have a 2008 Chevy 3500 LTZ. I have a message pop up saying service trailer brakes. First I check all the wireing,fuesses, and connections everything looks fine. Then I check the internet for advise people said change trailer brake relay. I change this part nothing happens. Back to the internet its probably the trailer brake control module so I change that but we you change that it has to be programed. Took it to the dealer where I bought it in 2008 they programed it for $104.00 said that wasn't it They said leave with us for a couple of days and they would find out what's wrong for $104.00 a hour. Has anyone had this problem.