Could be a bad sensor, or bad connection to one of them. The first suspect would be the coolant temp sensor the PCM uses..... (your truck only has one, it's either right to the drivers side of the thermostat housing, or, over on the passenger side, where the heater hose connects.)

 

Hmm, I wouldn't suspect that as it always has recorded my temp fine as long as Ive had it, sits right in about the same spot everytime it warms, and when I didnt have my fan shroud, it used to show it getting hot in traffic like you'd expect :/

 

My reasoning is, the temp sensor has the most profound effect on mixture ratio..... even an intermittent connection can cause trouble, and won't necessarily be reflected by the gauge in the dash.

 

Hmm, I'll check it tomorrow then and just unplug replug

 

Really? Maybe that's been my problem for the past 16 years. . .

 

Imho. It sounds like the cat is not flowing correctly. When I changed my it was after I replaced plenum with tune up. It ran like it had limited power, read some where on line that the cat should run at a certain temp range when warmed up. Mine was way over and when it was replaced I started for the first time at the repair shop and was blown away at how quick it started and how much better it sounded. It was a different truck. It must have been robbing power for a long time.

Also want to add, did the Hughes plate with OE pvc valve ( with tune up) about 6 or more yeas ago too. And at recent inspection looks like brand new still inside. I was not sure it would still look that good but it does.