I doubt gearing is a problem or it wouldn't be racing in the moped class. I bet it's a 318 in a /6 car witha stock diff.
After following RRR advice, and checking the kick down, I would check the fuel delivery and put a fresh filter on.
If your mechanic didn't see anything wrong then he must be a Ford mechanic.
I would start by doing a thorough inventory of what you have- engine #, tranny, rear end and gearing, carb, distributor etc. get to know what you have so that you can build on your mopar education.
