Okay I have a 94 5.9L auto. And I was on a long road trip alot of stop shut off the truck and then go again. And towards the end I noticed the truck doesn't sound the same. It didn't seem to have all the power it was kinda ******* a bit. I have a hollow cat. So I know it's not that. And I let it run when I got home and I didn't find any exhaust leaks at all so I'm kinda stumped. I mean the truck almost seemed like it was tired. Haha

 

How do your plugs look?
Like color wise. Engine running hot or cold?

 

They look good. I just replaced them not too long ago. 5k miles maby. It's just weird it sounds different. It seemed to happen right after I got gas.

 

I'd blame the gas until it's gone , replace it , and see if the same occurs with new gas from a different station , just because . That's really the only variable . We have a 98 5.9 jeep modded . It requires premium stock , we have the Mopar pref. PCM in it to boot . If I run a tank of 87 through it , it feels like I loose 20-30 ponies . Maybe someone screwed up the 'additive' mixture on that fuel and dumbed it down too much . Ya just never know . Seems logical given no real symptoms , and your last comment