I ran into that problem with the new 1971 Challenger R/T 340 automatic . My drive to work was about 58 miles one way . And 42 of it on interstate at 70 mph one way . The engine ran at that one RPM so much it got sluggish . I guess ring grove also. I had to start hammering it every chance I got to get it have a better response and pep. I don't remember what my gas mileage was back then . But I could drive to work and back each day plus other driving for about $2.50 a day. Think prem. was $.23 . But I didn't make much money back then . But had a good job at GE and made better than alot of people.