I was just curious as to why you would want to keep your engine at 3000 RPM, at that RPM your jeep would use more fuel.
Yes, but with the highest torque. The 4cyl usually peaks around 3000RPM in torque, and is therefore most efficient in the comparison between incoming fuel/air and output torque. If I drive 25mph, with the engine in 4th gear, and around 1700 RPM, I get worse gas mileage than running in 3rd gear, at 2600 RPM or so. (just as an example, I don't exactly remember which RPM goes where, as I HATE driving 25 and do it as little as possible).
Actually, because of the nixed cat on mine (PO did it, not me), my whole curve moved up (but gained an HP or two) and it's most efficient for me to run going way too fast for my driving brick, with the RPMs up even higher than most 4cyls.
When cruising fast, 35-4000 RPM is the best for me, I stay in fourth going up to ~75mph, until either my vibrating foot or my sense of well-being makes me shift to fifth (and this is with 215/75r 15's!, wait until I get some 30's or 31's!).
