That's about what I get in my ' 91 Carat, which is an automatic.
I try no to go over 75 mph.
You did not mention what you were driving?
Steve Johnson
' 91 Carat

I did not mention what I was driving because it was the 84 camper with the 2.1 big valve engine I have been sorting out and testing. I did not want that to change the conversation from milage to engine mods. 
I dont advise driving over 70 mph because it pounds out the exhaust seats. the big valve engine has harder seats installed same as I use in the propane engines so we will see if that helps. 
I am trying to dyno test again next week end the 23rd in hampton NH 
if you are interested call 
Bob
1 508 653 7229