Mitsubishi Repair Problems? Ask a Mechanic for Answers ASAP
Hi, This sounds like perfectly normal operation. With a final drive ratio of 4.235:1 and your fifth gear over drive of 0.775:1, calculating with stock tire size (215-45R18) diameter of 25.6 inches you should be turning just over 3000 RPM by 70mph. Take into account tire inflation (and so tire diameter) as well as gauge accuracy and you could see a 3-5% variance easily.
It looks like we missed each other. If you need more help on this just let me know and we can continue.