I have a 2006 Dodge ram 3500 with a 48re. When the truck was almost new I was going up a hill with a load of lumber on a 30 foot gooseneck trailer the transmission over heated. Now every time I haul something with a little weight it over heats the transmission. The motor will rev up but the truck just want go. When the truck is not hooked to anything it seems fine. The truck has 67000 miles on it. Any ideas on what could be causing this and what is the best fix.