I have a 2001, V6, 3.8L, 5spd Mustang coupe. Nothing too fancy. I just got it last week and right off the bat Ive noticed that 4th and 5th gear are quite interesting. If I shift into 5th any lower than 65mph, my RPMs hit 1500 and it does that loud shaking sound manuals do when there isn’t enough power for that gear. On the flip side though, I have to run 4th gear literally everywhere except the highway. Typically I’m at 50+ MPH so my RPMs are ALWAYS at 2500+. This is obviously a huge gas guzzling issue. This is my first mustang so I was wondering of this is every 5spd mustang or if this is something that is wrong. In all my other manual cars, I could hit 5th gear at about 45 or less and be just fine. Is there anything else I can do to increase my gas mileage (other than the cold air intake already done that one)?