Runs fine in Park and Neutral. Runs so poorly it cannot move itself in D and R.

2001 5.4 Ford F150 was running fine and then suddenly became undrivable. In park and neutral, truck runs normally. Starts right up, idles smoothly and pressing the accelerator will result in the engine smoothly running faster, RPM can go all the way up the safe range. In gear, things are very different. Truck runs so poorly that it cannot move under its own power. No codes in computer, according to a shop I towed the truck to. Check Engine Light is on. Overdrive Off light blinks constantly and clicking Overdrive button on gearshift knob does nothing. Checked fuel as it comes out of fuel filter because some people suggested that it might be fuel starvation but fuel flow out of the filter seems ok. Sprayed starter fluid in air intake and truck ran good enough to move while starter fluid was being applied which makes it seem like fuel starvation again. Once the starter fluid was consumed truck returned to running too poorly to move itself again.

Any ideas why and how I can fix the problem?