1997 Mitsubishi Galant 116,00 miles

I recently purchased a car and I was told by the previous owner that the transmission was rebuilt in it and it had slight problems with accelerating on turns uphill. Well, I've been driving it all week and it seems to have trouble accelerating in general. My previous car was the same make and model but a 1996. I would get almost 400 mi. per tank. This car only gets 250 barely. And the whole time I'm driving it, I have my foot constantly on the gas. Even if I speed up, the car doesn't really coast. Also, the RPM always seems high to me. When driving the cars RPM ranges from 2500 to 3000. Does that seem normal? In order to go 75 on the highway it is almost 3500. The car feels like it is struggling. What could be the problem? Please don't say transmission.