03 is the split year for ford f/e 250/350's so it depends on what trans you have (4r100 or 5r110w). does it have all the forward gears ok? it could be something in the valve body or something stripped out inside. the later model (5r110w) has a common problem with reverse, ford designed the reverse circuit to have about 450psi and put an extremely weak snap ring in it so the snap ring pops out and you lose reverse. when the snap ring pops out sometimes it will break the case, is it leaking by the back of the case? i work at a trans shop in snohomish and i can help you out if you want to. you can call me at (360) 568-0220 ask for Jaden