E85 Engine

I have a 2002 Tahoe with a 5.3 L, E85 engine. My fuel economy is @14 mgp. I previously owned a 2000 Tahoe that was identical except for the engine was not the E85. The fuel economy was @ 18 mpg.

I don't run Ethanol because I can't buy it in my area. Should these two vehicles get that much of a difference in fuel economy? Can I change something on my E85 engine to make the economy similar to my 2000? Again, both vehicles were exactly the same except for the E85 engine.

Thanks for the help.

This is my question also.

My current is a 04' Z71 3:73 Gear E85 motor and stock tires. Its got like 9k on it and I get 13.5-14 city / 17-18 hwy.

The last one was a 96' LT 4X4 Tahoe with a L30 motor( stock 350) / 4:10 gears. It got about 18 city almost 20 on the hwy??? stock tires also.