I have no personal experience with these ....but your truck could be a candidate for one of these:
http://www.forddoctorsdts.com/articl...icle-05-01.php
Overdrive for Ford E4OD & 4R100 4 speed automatics Save Money!
When they offer one suitable for the f250 6.0 with transfer case ,i intend on getting one or the other.
If you do a "payoff analysys" dont be short sighted...you can do the install with the thought of taking it with you to your next truck ,years down the road. or reselling it with your truck at a markup. (Keep your original parts AND modify a junk yard driveshaft that you recondition)\
I dont have personal experience with your engine. I am certain that mileage drops off
big time ,when i cross over the sweet spot of 2000 rpm on my 6.0. Hopefully others will chime in what there experience has been with your model engine.