Now just to start off with, I know suburbans are not world-renowned for their gas mileage! I just picked up a 1988 suburban with the 350 engine and turbo 400 3-speed transmission. Besides sitting unused for the last 3 years, it's in good shape. I've run some Seafoam through it, as well as some injector cleaner. I also today just cleaned out the throttle body. It starts right up, and after cleaning the throttle body, the low-rev hesitation seems to have gone away for the most part. All in all mechanically it seems to be running well. After running my first tank of gas through it, I registered around 9.5 MPG with mostly freeway driving (55 - 70 MPH). Today I did a quick test run. I ran it on the freeway after filling it for about 50 miles and only pulled 8.7 MPG (averaging around 68 MPH), far below what I consider acceptable. My Dad's old suburban in the past pulled around 15 MPG average, so 8.7 is unacceptable. Other notes - The CEL only came on once after I first drove it away, and went out after about 10 seconds. I figured it was just running some old gas through the engine and that tripped a sensor. After cleaning the throttle body today, the CEL again came on for about 10 seconds and then went out again. I've noticed a slight engine ticking at around the 60 mph range. If I speed up to 70 it goes away, and if I slow back down below 60 again it also goes away. Sometimes it ticks (definitely affected by the rev's on the engine) after driving at 60 and then exiting the freeway, but the noise usually dissipates after a few minutes. Not sure if that is related or not, I just figured it was some valve noise. Any ideas as to why my mileage is so bad, and what else I can do about it? Thanks in advance.