I have a 1999 F-350, 2 wheel drive, 7.3 and 4R100 trans. The other day when it should have shifted into overdrive it acted like it had no overdrive. I mashed the OD button and it went back to drive then it went into OD. Today when it shifted to OD it slowed down the truck like it was hung in two gears. Once again I pushed the OD button off and it went back in drive and seemed fine until I tried OD again. It feels like it holding the truck back. Any idea what this could be?