my original owner 2006 diesel 4wd automatic with 131000 miles started acting up, when on a short trip to pick up something light maybe 1 1/2 ton plus light car trailer, the truck will not shift into second until it hits 2500 rpm now, no other issues except a slight shutter when coming to a stop, i baby this truck, about 40k ago i replaced the transducer and the govenor solenoid with the alison style, also put in an "extreme duty pressure solenoid manifold" at the same time, that all worked great until now, any ideas what could be wrong?