A mild surging of the engine between 1400 and 1800 rpm.

Under the hood of your truck there should be an emission decal showing the various routing of the vacuum hoses for your engine. Look at the decal and follow each hose. Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info. There is a company that independent auto repair shops get their information from, this same information is available inexpensively for people that work on their own cars.. The information is year make and model specific, covering repair procedures, torque specifications, fluid capacities and specifications, service bulletins, component locations, wiring diagrams ect.... Alldata is very easy to navigate http://bit.ly/AllData_Repair_Manuals_Online

To add to my friend Pat, the egr valve may be opening and closing causing this condition. remove the vacuum line and road test to verify. if it stops you need to have the control side checked out. Roy

they're all wrong answers it's the vacuum canister is rotted on the bottom take the canister off and use Epoxy, reseal it and wire tie it back on the fender,The thing that looks like a coffee can