E-28 is for the camshaft position sensor signal circuit malfunction,if replacing a camshaft sensor it is also recommended to also chang the crankshaft position sensor.
Could be that the truck just needs new plugs, also Does this have the K21/K25 engine in it? How many hours are on the truck? Full Model and serial number?
Another possibility is the wires going into the sensor connector(broken wires),especially if a bunch of stretch wrap of floor debris gets sucked up into the engine compartment?