I have a 2010 GMC Sierra 2500 HD with an integrated brake controller. The controller manual for the adjustment states to pull the trailer between 20-25 mph and apply the Manual Trailer Brake lever, adjusting the trailer gain just below the point of the trailer wheel lock-up. It then reads “Trailer wheel lock-up may not occur if towing a heavily loaded trailer. In this case, adjust the Trailer Gain to the highest allowable setting for the towing condition.” What does "highest allowable setting for the towing condition" mean. I Have a Greystone 29MK, weighing about 9,000#, and wonder if the trailer brakes will lock-up or is it too heavy and if not, how to adjust the controller.