As far as gas mileage goes, as long as you don't drive at WOT all the time, it doesn't matter what RPM you shift at. At part throttle, the computer will dispense as much fuel as necessary. The problem is knowing how much pedal pressure is considered WOT. If you floor it and shift at 3000 vs. aggressive part throttle and shifting at 4500, you'll get better gas mileage with the latter. There won't be much difference at all between granny driving and aggressive part throttle driving if you shift at the same RPMs. In fact, if there is, it is likely that the aggressive driving is more efficient. It also keeps the injectors cleaner.
The driving like a granny is better for carbureted cars since they don't manage fuel efficiently.
This is important since I'm tired of seeing Mustang owners drive like grannies for no reason, especially if they're in front of me.
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351W 89 Mustang GT Convertible