We have a 440 with lots of tweeks done to it (aprox 425 HP). Have a 750HolleyDP on it. we moved from an elevation of 4000 feet to 300 foot. I've had problems ever since. Changed the front jets to bigger, and got rid of most of the hesitation in the launch, but now have a bad Bad miss fire (maybe backfire) after I hammer it in 1st gear (well in all gears (auto trans). Do you think the power valve might be bad?