1990 Iroc L98 with trick flow 65cc/ 195cc heads, LT4 hot cam, and hooker headers. tuning issues, car runs very rich and mpg's are terrible after the mods. I basically need a good tune if its possible on the stock ECU? any suggestions?

Change to EBL P4 and learn to tune yourself. Very hard to beat on a factory-ish SD TPI car. I feel like I'm just pimping someone else's product but it works.