So, a couple years ago I noticed I was running higher RPM at a given speed than I used to and thought it was my torque converter giving out. Then a couple weeks ago I moved my scanguage over from another rig and noticed my tach reads about 12% higher than what the SG / ECU does. So what I can't figure out is why the tach signal would suddenly (two years ago, but it did happen quickly) have less resistance at the gauge (right?).

 

I have an Ultraguage (not a Scanguage) . For it to work right, it has to be configured to match the specs of my rig (V6 or I4 , for example). Could that configuration have gotten messed up?

 

Don't think so. The scangauge reads the same in both my 5vz powered 4.30 geared rigs on the same size tires. But one of the tachs is 200-300 RPM higher on the highway.