engine cutting out down track after in 3rd gear!

I had the exact same problem with my Carter high flow mechanical fuel pump. 1 & 2 pulled great, but as it shifted to 3rd, the sustained RPM's overdrove the fuel pump, which raised the pressure enough to overcome the float pressure on the needle valves in the carb, and the engine would flood. The Air/Fuel ration just kept getting richer until is suddenly went to 0, which is 100% fuel, LOL.

I put on a good quality regulator, and keep the pressure around 5 psi, and problem solved. I am running a Thermoquad, which is a little more sensitive to fuel pressure that the Holley.