Are you getting a flashing O/D light? If so then you need to have the truck hooked to a scanner. I would be suspect of a bad solenoid pack. I just put a new stage 3 trans in my truck and the company I bought it from had gotten a bad solenoid pack that they put in then when I put the trans in I had to have them send me two more until I finally got a good one. They ended up ordering a new one from ford for me. The reman company they were using named Recon has very poor quality control. I wouldn't get one from them. Moral of the story is that ypu either have a bad solenoid pack or an internal seal failure. The pack is easy to change. The seal would require a tear down though unless your valve body is sticking in which case you could swap out valve bodies.
97 F-350 XLT CC DRW 4X4 PSD, 285/75-16 Custom bumpers, Gauges-boost/egt/trans, Swamps IDM, 3.5"dp- 4" exh., 3" Body lift, ES bushings/mounts, Built trans, billet conv, B&M pan, Hayden cooler, Adrenaline, stage 2's, IC, H2E, E-fuel
ARP's, 910's, Smith Bros. to come