Unplugging the CPU will NOT make your A/F drop back down. For all you know it could make it leaner. If it was as simple as unplugging your CPU to get your A/F to 13-1 then the tunres would be out of buisness.
Anyways either just buy a diablo tuner and add some fuel and have it tested again...if its still lean, then add some more fuel and do another pull (your basically the tuner). And were you making 275RWHP in that dyno? Another option is to go to another shop, Tim at MPH will charge under 600 for a complete dyno tune with an SCT chip....those guys are ripping you off.