Is your check engine light on? If so, have the dealer check the computer for a fault with the trans. pressure switch. I had this issue with mine last year. Although my 98 is only a half ton, I'd be willing to bet the electronic "little things" inside our tranny's are very similar. I had the exact issue you describe at about 65,000 miles. Came on at LOTO last year. Dealer there re-mapped the computer to get me home (they did not have the parts needed, two small switches inside the tranny, accessable from the tranny pan). Once home a neighbor is a Dodge tranny guy and got me the parts cheap and told me how to fix it. Been fine ever since. Now have about 102,000 miles on it.