Kind of like something is dirty. What can I start checking/cleaning to get it back to normal.

I've only had since mid November, this is the first "warm" day I've had it. it's 53* out and Sunny. Took it to town and the rpms are moving up and down a bit. Barely doing it but it's very noticeable. Speed doesn't matter. From the moment its moving to 55mph cruise the rpms will kinda move +/- 50-100 rpms of where they should be.

Starts perfect. Idles perfect. Plugs were changed 6 weeks ago. New fuel pump and filter about a month ago. Bad EGR Valve and Sensor are my codes but that's since I've had it. Fuel mileage is 10 and has stayed 10 almost no matter what type of driving I do short of plowing a lot on that tank (where then I've gotten 6)

Almost like Tranny could be slipping truthfully. It's an automatic with 128k miles.

 

My truck does something like that. In overdrive it is turning just over 1700 rpm at 55 mph. Sometimes it gets quiet and smooth and the rpm drops to 1500. It usually doesn't last very long, but it seems like that is the way it ought to be. The only code is "canister purge circuit failure".

 

Anything emissions related can and will destroy mileage. CHECK the sensor and EGR valve to see if they are actually bad. If they don't pass, change them out. Otherwise, replace all of your vacuum lines. Make sure they're routed correctly, too. People love messing with vacuum lines and then selling it because they can't figure out what's wrong. There is a sticker under the hood showing the correct routing for your truck.

 

Can u feel the rpm's change while driving? My aftermarket tach bounces +/- 500 rpm going down our lovely (lousy) Louisiana roads. A cheap aftermarket tach will do that. I only gave $20 for my tach but it works well enough and has seven LED colors to boot. It looks coooool. Lol

 

Rpms stay around wherever they 'should' but kinda bounce like I can't keep my foot steady on the gas.

Don't have Emissions in MI. I checked the codes myself and the only 2 I got were Sensor and Valve. Light only comes on after it's warmed up a little bit, which makes sense since the valve would want to open then. I got the truck in November, but It was my parents plow truck since about 1998 when we they bought their house and got the truck. Rarely left driveway and parked in garage when it wasn't snow season.

Definitely can feel the rpm movement. Can feel the truck slow a tad like got off the gas for that second. Can hear it too, especially since I have an exhaust leak near the manifold so it drones a lot around near 2k rpms.

I'll have to get a video of what it's doing.

 

iv always heard if the tach bounces (and its not a bad tach or sensor) its the transmission slipping, but id definitely keep looking into it, thats just the only thing iv heard of causing the tachometer to bounce.

 

It didn't it a couple times only once or twice but not anymore. Was a good 40 minutes of driving. <scratches head>

Temps today, 44* and raining.

I'm wondering if I burned the fluid so it's acting up. I had a lot of heavy snow plowing a few weeks back and I notice it getting doggy. When I was done I felt the tranny and the pan was too hot to even touch. I normally plow in 4 low since the 3 driveways i do are small and don't even need to get out of first gear. But my parents driveway is long so I need to keep speed up.