2001 Tahoe mpg keeps getting lower

Folks,

I take good care of my car, and take it to the dealer for every oil change and service. In the 1 1/2 years i have owned my car, it has gone form 16 mpg to 13 mpg. I mention this at the dealer and they say all is well, but i can see black soot at the end of my tail pipe and a little on my rear bumper. I have had the spark plugs replaced and same result. I have about 100k mile on my car. Air filter, fuel filter peplaced in last 15 k miles, same result.

Any thoughts?

Sounds like your engine is running rich. The computer is responsible for making the engine run leaner or richer. My truck was getting a bit clogged in the injectors. The dealer had to flush(clean) the injectors three times back to back before the sensor allowed the engine to run leaner....good luck

What engine?
Has the fuel pressure and fuel regulator ever been checked?
What kind of plugs did you feed it?
Did the dealer put it on a scanner and check computer and sensors?
Have you changed tire sise or done any add on stuff?
Did it drop all at one time or slow like?
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