Class A V-10 mileage

I have driven the same MH in my signature a little over 100,000 miles and have tracked every fill up over the last 15 years manually. I tow a 2500lb Toyota Corolla most of the time. I don't notice any MPG difference towing vs not towing. Added headers and FF muffler. No difference. Added CAI sans cat. No difference. Advanced base timing from 4 degrees BTC to 9. Slight difference. Each mod improved performance but not MPG. Performance went from 19 sec to go from 40-60 mph down to 12 secs. Went from down shifting at the slightest hill to staying in high gear in all but steep hills out west. There were several things that I observed that increased my MPG slightly. Keeping my speed between 55 on backroads and 62 on the highway increased mpg from 8 to 8.5 . Adding a vacuum gauge and keeping vacuum above 10 in HG. Also increasing speed when approaching a hill then letting off the throttle to keep it in high gear. I know when it will shift by watching the vacuum gauge. This increased my mpg to 8.7 mpg. Having said all that I like the increased performance over the mpg gains.