Gas millage dropping down from 18 MPG to 15 MPG

[CARC686]

I'm not sure about OP, but I'm at sea level and I have a turbo. Still gets 14-16 mpg.

And I don't have any mufflers and it's terrible. The downpipe comes off the turbo and dumps right behind the passenger front tire because I haven't had time to make an exhaust, and it's the loudest vehicle I've ever driven. Including my 396 small block Corvette with side pipes...

Another peculiarity to my truck is that the IP timing is extremely advanced, but the Warhorses guys will tell you that you have to do that with a HMMWV pump on a NA 6.2 anyway because it's the wrong pump. For me, it was the right pump because it was new in box for $700. If you start feeling like your Vette is too loud, I'll keep the seat warm for you.