So I’ve been dealing with this issue for some time now. I went out and started it for the first time in two days so it was pretty cold.Once I fired it up it revved up super high then fell back down and just loped super hard for about 3-5 min till it got some what warm. So I let it idle a little longer,I touch the throttle in P and it started loping again!!!!But if I keep my foot on it at a steady 900-1000 RPM is does just fine.Now if I press the throttle anymore the truck will start spitting white smoke and doesn’t rev up at all.Itll just shake and spit white smoke.Ive been stuck on this problem for two weeks now,please someone give some info. Thanks!!

 

White smoke is unburnt fuel, timing is off or a bad injector.
Along with your other post it would seem you may have air getting into the system.
Need to check all the fuel lines from the tank to pump.
Before starting crack the inlet line or return line to the injection pump and hand operate the lift pump and check for air in the system.