No, you can and should use high mileage oil if the vehicle has over 100,000 on the ODO.
My car has SUPER great mileage! It has the best mileage ever!
Make sure the car is equipped to make the journey.
Your 2001 LeSabre is rated at 20MPG City/29MPG Highway. I've found this rating to be fairly accurate. I average 20-22MPG when I'm not using the A/C and have measured highway mileage at just a shade under 30MPG. Pretty good for a big car that has a little pep.
No, it will decrease gas mileage.
Better mileage
Finding the best mpg suv will depend greatly on your lifestyle. Using the comparison sites can help you to decide which SUV will offer you the best mileage based on the way you will be using it.
Most hotels are now equipped with WiFi. There's no need to use dial-up internet connection for that even if they're using virtual PBX phone systems. Take advantage of their hotspots.
The fuel mileage of the new cars far exceeds that of the older models which makes them more economical to drive.
No
No, not to any degree you will notice.
It lowers your mpg
The supercharger will do this automatically. When cruising the supercharger vents pressure and the vehicle operates similar as though it is normally aspirated using much less fuel. If mileage drops off you might want to verify whether or not the bypass system is working.