Are you running an automatic in that thing? If you are and are using the stock torque converter that could be your problem. The stock converter will work against the engine that you have in there, until you get into your power range (2800 - 8000). One of the other thing that you might try doing is adding a little more air into your idle circuit by drilling a 1/16 hole in the primary butterfly of the carb ( I'm assuming that your running a Holley). Changing the pump shot should also be considered. Just a few considerations to make, hope this helps.