If your engine sputters and slowly idles down till its about to die its loading up and probably to rich. The first problem is 2 fold, you have an engine now that has a lot more top end power curve than your old engine. The transmission will need to be adjusted to shift at a higher speed. After that you can trim out the engine for preformance. The XTM specs for that engine is about 4k higher than your stock engine. Or at least it sounds at least that much higher.........good luck m8[:-]