96 OBDII Reprogramming

I live in Denver and at this altitude the cars up here don't run with a lot of power. I understand that altitude effects performance, but I know the engine is running rich. The truck came from South Carolina. Does anyone have some suggestions for a product that I can use to reprogram the air/fuel mixture? I know about Hypertech already. Unfortunately, they have a set program that is good at lower altitudes, but won't do much up here. I am looking for something that will allow me to make UNLIMITED modifications through the OBDII diagnostic plug. That way I can tune it more precisely. Please let me know. Thanks in advance.