this is one of the trucks i drive at work- its a 2001 ram 4x4 360 auto. I`ve been told its the 3 trans its had in it. it shifts fine when its cold but after 5 minutes of driving it does not want to shift. if I shift it into neutral and then back to drive it will shift into the next gear. there does not seem to be any slipping at all in any gear. any ideas?