You didn't say what your rear end gears were. I am assuming stock 2.73's or 3.08's. With that tire and a 2.73 gear, you should be turning about 1800 at 75 mph. With a 3.08 gear, you should be turning 2000 RPM at 75. Then again, you have different tires than stock too. So just go for ball park figures here since your speedometer is off a little too. As far as not going into od, check your tv cable. You can do a search on this site for it, as there have been several threads about it. I am not much of an automatic guy, I like changing gears on my own. It's too much fun.
If your car is turning 2700 at 75, it has 2.73's in it. If it is turning 3000 at 75, your car has 3.08's in it.
