If you've got no SES light.... then go ahead and plan on swapping out the fuel pump.
If it's running better now, then remove the fuel filter and key the truck on and note the fuel flow. Should fill the bowl completely in short order. If it's just a trickle, then you may have something clogging the line.
If it starts acting up again, key it on and lay your hand on the pump (under drivers feet on inside of framerail). The pump will cycle for 20 or so seconds each key on. If you feel/hear nothing while laying under the truck with your hand on the pump then it's done. Get another one.
If you do feel/hear it running, then pull the filter and key it on to check the fuel flow again. I expect it will be nothing, or a slight trickle.
The power required to run 50mph or so is juuuuuuuuust about as much as the injectors can syphon from the tank in many cases.
I would start by ensuring your fuel delivery system is performing as it should. Your description screams fuel starvation to me. Especially with no SES light. I'm assuming of course that there is plenty of 15w 40 in the engine.