[FF777]

In November 2007 I was given a 2000 chevy prizm by my grandparents with 110,000 miles. The car now has 180,000 miles on it and I recently did a tune up (changed spark plugs, oxygen sensors, catalytic converter, tranmission flush, air filter, battery, pcv valve, and oil and filter change). I inflated my tires to 40 psi, took out the back seat and emptied the junk out of the car. I go no faster than 50 mph on the highway with windows up. There is some minor body damage to the front of the car but I dont think it makes a whole lot of aerodynamic differnce since I'm only going 50 mph sometimes even 45. My RPMs at 50 mph are around 2400-2500. This is high as I test drove a 2004 corolla 4 speed automatifc and it was doing around 2000-2100 at 50 mph. I'm averaging 31 mpg combined over a tank of gas. I guess that's good for a 3-speed auto but I want 40 combined. I called tranmission shops to see if there was a way to swap my 3 speed auto for a 4-speed auto or 5-speed automatic but they all say its not worth the expense. I was thinking of purchasing a scan gauge so I can see the optimium fuel efficient speed my car travels. Shoudl I reduce my highway speed to 45? I goal is to consistantly get 40 mpg combined in my 3-speed automatic prizm. It seems my transmission is holding me back. Is there a way I can get my rpms down without spending thousands of dollars? Any suggestions?