[JLMounce]

If there is evidence of a cam swap, it may have reduced your low-end torque slightly. Coupled with the weight of your GTO and your gearing, I could understand the car being a little sluggish off the line, but moving nicely through the gears.

Your M20 should have a 2.52 first gear. Multiply your 3.23 rear gear and you get an effective starting line ratio of 8.14:1. Most performance street cars with lower power, would prefer a 9:1 to 11:1 starting line ratio for maximum acceleration out of the whole. If you've got very tall tires on the car, that makes the effective ratio even worse. The factory tire would have been between 26 to 26.5" in diameter. A modern 27" tire is usually used.

The easiest way to skin that cat would be a gear change. A 3.55 gear gets you just under 9:1 starting line, while a 3.73 gets you solidly to 9.4. You'll notice much better first gear performance by doing this, at the expense of highway cruising.

For a best of both worlds approach, you can keep the 3.23 rear gear and go to a wide ratio TKX. You get even better highway cruise ability and the 3.27 first gear gets you a 10.56:1 starting line ratio. That would completely transform how the car behaves.