Hey I’m new to the site. I have had several duramax trucks from 05 2500 to 12 2500. We use these trucks as a pice of equipment. So I hate to say they all get ran hard. We use them to move our tractors around they always are pulling a trailer. I always try to do all repairs my self. My 09 3500 4x4 220000 miles just started for no reason without a trailer hooked up will put out full trailer gain. You will be driving down the road and look down at the message center and you will see full gain. Just driving down the road not pressing the brake or anything. So I tried sliding the manual switch back and forth but nothing. It will also do the same thing with a trailer. Cost me a set of trailer tires. I’ve set the gain to 0 so it will not lock up the brakes but it will still every now and then put full power on the dash. Never had the check engine light come on or service trailer brake. I can’t find anyone that has had this issue? Any ideas?