Q&A

Its not a good idea to replace parts without without testing the component and seeing it is faulty. Could it be a transmission failure (or a slipping clutch if manual transmission)? A professional grade scantool would give better testing capabilities in being able to read actual figures of air going into the engine and other inputs and out puts from the vehicle's power train computer. It's hard to guess what is the problem with your truck without being able to do some diagnostic tests and experience the problem first hand.
Do you have service manual for your truck to get test procedures?
There are two companies that independent auto repair shops "buy" their information from that offer a very reasonable service to do it yourselvers. You can get a one week subscription or year subscription very cheap. The information is year make and model specific repair procedures, service bulletins, component locations, wiring diagrams ect.... great quality information same as the professionals have,much better than generic workshop manuals from parts stores and much cheaper than the factory manual try Alldata which is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online or Mitchell on line http://bit.ly/Mitchell1_Online_Repair_Manuals and get an online repair manual subscription. Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info.
and get an online repair manual subscription.