Man there are about 100 things that could be causing it to be down on power. Start with the basics and keep working deeper and deeper until something is discovered.
-Induction system: check for vac leaks, throttle body function, inlet pipe system sealed, MAF working, filter clean, etc.
-Fuel system, check system pressure. Have injectors tested (more advanced)
-Exhaust - is it free flowing, no restrictions? was it crushed by Midas when they tried to jack up your truck? etc.
-Lubrication - Got oil in it?
-Ignition - change plugs, it is not that hard. Dont cheap out, get the OEM NGK ones.
-Transmission - any CEL codes? shifting OK? enough fluid? fluid look a good color? Is the transmission in limp mode? (would cause similar symptoms to what you are seeing). Do you have the milkshake of death happening (ATF mixing with coolant)?
Beyond that, take it to a mechanic.