Transmission problems

[capttonyray]

The other day I went to back up and it felt like the parking brake was on, then 2 other times i put it in reverse and it did not move, went to drive then back to reverse and it worked fine. It also does not shift to OD all of the time you hane to let of the gas to get it to shift. The vechile is a 2003 Excurision with a 7.3 liter diesel. any suggestion would help, I'm getting ready to tow a 10,000 lb boat and want it right.