2011 Chevrolet Avalanche when hauling a trailor

when I am hauling a trailer with my 2011 avalanche when I stop and take off there is a loud whining sound not all the time heavier trailer loads make it do it more often this will also cause the rpms in the vehicle to jump alot I took it in and they told me that it does shift hard but that is normal but everything is fine the last avalanche the transmission went at 70000 the low gears went out hauling a trailer I don't know what to do . My brother is a certified mechanic and he told me it sounds like the pressure control solenoid and the planetary gears it is under warranty but they say if it don't do it when its in the shop there is nothing they can do I just wanted another opinion on what it could be