Originally Posted by DeathRattle
You will def need a tune. I would not recommend driving that car without one. You can get a canned tune, a custom tune, or a dyno tune. The cheapest route for a Mustang with basic mods is probably a canned tune. You can find used tuners for like $150 shipped if you search Ebay and Craigslist. Stick with Diablosport or SCT.
Does the tuner correct the shift points even with a stock transmission?