I currently average around 22-23 mpg highway
The 99+ manifold is in the works actually. I already have it; I'm just waiting to be able to afford a Banks header and exhaust wrap before I install it
There's a couple of things I have noticed since having a scangauge. My gas mileage is really terrible when my engine is cold. I really want a block warmer but I live in an apartment right now. I also get terrible mileage while accelerating, so I think that mods like the newer manifold will help a lot.