Let's face it, a lot of us Mustang owners have modified our engines to increase horsepower. However, this usually means reving higher than the C4 tranny automatically shifts at to utilize the extra power. I have the C4 tranny and despite several attempts to adjust my vacuum modulator with my transmission mechanic, my tranny won't automatically shift higher than it's typical 4,500 rpm without hard damaging downshifts while coasting. I can manually shift to reach 7,000 rpm, but I prefer my tranny to do this automatically. I guess my only option is to purchase an electronic transmission. I prefer an AOD (4 speed automatic overdrive) electronic transmission. The overdrive would also be nice to reduce my high 2,800 rpm while driving at 60 mph. I don't prefer a manual transmission. I own a modified 1971 sportsroof Mustang. Is it my only option to replace my C4 with an electronic tranny, and if so, what transmissions do you recommend?