From what I recall, the J4J1 (Cobra) tune is typically more forgiving of mods than the T4M0 (GT) tune. I'm running them on my GT now with very few drivability issues. It's more so the cam that freaks them out, but nothing that can't be tuned out. IIRC, anything below a 112° lobe separation angle on the cam is what starts the headaches.