only other thing i can think of off hand is the map sensor ,, if you have already checked all the vacuum lines from the engine and to the vapor cannister under the drivers side of the truck at the frame rail , and the plugs on the sides of the intake for leaks ,, then that could give you problems as well - do the voltage test on it as described in the haynes manual or use a scan tool to check its readings , hope that helps !

 

ok , one more thought ,, maybe the pre-cat o-2 sensor is mal-functioning some how and just isnt throwing a C.E.L. yet ??

 

have you pulled your tb off and cleane it yet. you might have a bad iac motor to. while you got your tb off look down your intake and see if theres oil built up in the back of your intake. if there is thats where your chugin is comin from. blown palinium gasket.

 

where is that sensor located at I picked some acetone for the injectors I kinda slacked on that this winter.
vacuum is good
timing chain is original

 

its on the back of the tb. its a lot easyer to pull the tb and clean it while your at it. you can take the iac motor out of the tb and clean it to but from what i hear it dont last long befor it will clog up again. i guess its best to just replace it. but if you pull it and give it a good clean with for carb and choke spray and it runs better then you know