Could I buy a pre tuned tuner for a 2008 mustang gt/cs built 4.6 with no build sheet information? It has a nitrous system in it that I've never used. When I get on it hard it backfires and cuts out. I tried a Diablo tuner but it didn't help and now it runs terrible. It ran great before the Diablo tune. Please tell me how can I fix this problem. The big tune shops can't help without the build sheet. This car came out of Saint Peter's Mo.