Originally Posted by 01C0bra
What would be my best choice? Taking it to a performance shop to get it tuned or buying an sct tuner?
What also wonders me is that it still ran about the same when I had the stock intake on it.
Return it to stock while you are diagnosing your issues here.
First, if the car is shutting off in neutral or while coming to a stop - replace, do not clean, your idle air control valve. It's an inexpensive part that commonly fails and cleaning is a temporary fix - if a fix at all.
Next, a vacuum leak isn't going to just hurt you in 4th gear trying to mash the throttle - you'd know it at all times.