Ebay GT45 + 5.9 Magnum + E85 blow thru

Tuning with an exhaust leak will make you pull out your hair. Ask me how I know. Make sure the exhaust is buttoned up tighter than a dolphins *** before you start making any air fuel target changes.
Yep. I won't even start tuning until it's solid. Learned my lesson with the Fitech. Most of my tuning problems were due to a leak somewhere before the O2 sensor and I'd chase my tail for days trying to get it to behave just to discover I had a tiny leak in the hotside. I'd fix it and everything would just fall into place.