Your calculations are correct, and yes it is possible to use taller gears than the 2.88 gears that you currently have, however, it is probably not in your best interest to do so.

The problem occurs with horsepower. The substitution of 2.88 gears has reduced your available horsepower by 6.25% at a given speed. You will notice, out on the highway, that pressing down on the pedal at 65 mph yields noticeably less response than what you originally had with 3.07 gears.
However, and this is important, the required torque from the engine has increased. Why is this? Well, the required torque to the pavement has remained the same at a given speed and the available torque to the pavement has decreased by 6.25% because of the gear ratio. So, the only alternative is to increase the torque from the engine by 6.25% to compensate. So, with the increased torque from the engine comes higher exhaust temperatures across the operating range.

This is the main reason that you will not get anywhere near a 6.25% increase in fuel efficiency by switching to the 2.88 gears. The engine has to work harder to push the vehicle at 65mph and it requires additional fuel to do this. Now, there are some benefits of running the engine slower due to reduced frictional losses within the engine. You need less fuel to run the engine at 3000 rpm than you do at 2700 rpm, all else being equal.

I can tell you my personal results of switching from 195-70-14 tires to 215-70-14 tires. The reduction in engine speed is about 3.5%. I could not measure any difference in fuel economy after the odometer was properly corrected for the larger tires.