I used to get 5-6 mpg all the time, but my truck would only go 75 MPH. 
My Brothers Pete on the other hand would really ROCK!! I was driving it for him one day when I realised I had another gear. I was doing 75 at the time. :-laf 100+ no problem.
When I was picking up someone at the airport, I had a "large car"behind me in the turnpike. I was going 85, and I was really holding him up. I pulled over and he flew by me. At times he was well over 100. I kept with him (@95-100) for a few minutes then stopped.

My Brothers Pete on the other hand would really ROCK!! I was driving it for him one day when I realised I had another gear. I was doing 75 at the time. :-laf 100+ no problem.
When I was picking up someone at the airport, I had a "large car"behind me in the turnpike. I was going 85, and I was really holding him up. I pulled over and he flew by me. At times he was well over 100. I kept with him (@95-100) for a few minutes then stopped.