I disagree on the two different issues, one electrical for the brakes and one mechanical for the lack of power. This really sounds to me like his Chevy electrical has a problem and is applying voltage to the trailer brakes and here's why I think so.
One test of an automatic transmission is to check the stall speed. You press very firmly on the brakes and then floor the accelerator while watching the tachometer. The engine will rev up into the two thousands range and stay there as it tries to overcome the brakes and move the vehicle. So I can fully see where the Op's truck is not able to rev past 2500 rpm if his truck is applying the trailer brakes.
phiko73, When the brakes seem to be dragging is it a persistent problem or does it come and go. If it's persistent you could try pulling into a parking lot and park. Go put your ear near a wheel and see if there is a hum sound from the brakes being engaged. If you hear a hum it means your truck is feeding power down the brake line. You can verify this by having somebody unplug the trailer from the truck while you listen for the hum. If it goes silent you have verified that the truck wiring is somehow faulty and keeping the brakes on.
Also, if I am correct and the 2,500 rpm limit you are experiencing is the trailer holding you back then your transmission torque converter has been slipping which is normal, but can generate a tremendous amount of heat in a very short time. This can significantly shorten the life of the transmission fluid. You will probably want to get the transmission serviced to get the fluid changed if you're taking it to the shop anyway.
