Rough running Ram

I have a 98 dodge 1500 it seems to run rough at times. At an idle it seems ok for a while then it starts to run real rough RPMs drop to 200 then it works itself out of it a couple of minutes later running fine again. going down the road at 20 to 35 MPH I can here it sucking air and if i feather the throttle it surges and sometimes it back fires. Ive had the plugs, plug wires, rotor cap, fuel pump and intake gasket replaced. Anyone have any suggestions

try looking under the battery box at the cruise controll pod see if the the vacume line is rotted out ?