mach is jerking while driving.

[ASH302]

okay, trying to figure this out, maybe someone can post a thread of this. but the mach I just got is having some issues already that it did not do while test driving. Just a little back story, it has Dss Racing 5.0 and cams, other add ons and been dyno tuned.
The guy selling it said that he really hadn't driven it for a year and half and would go from time to time to start it up and let it run, do not know how often. Before I bought the car, I asked him to do a oil change and compression test. I have the paperwork to show that he did both those things the morning I went.
I went and test drove the car and it acted fine.
My road trip home was over 3 hours and about an hour into the trip, I had to take the exit, when I pushed in the clutch the car dropped rpms and died on me. I had to start it right back up. I had this problem in my other mach and we either retuned it or i changed the IAC.
The next thing that it is wanting to do and did not do this while test driving is jerk really bad while barely pushing down the throttle to hold speed. jerking meaning it is cutting out, skipping that drip of fuel to keep it steadly going.

Has anyone dealt with this? again the car basically was sitting for over a year and the guy said that it had no issues like this when he got everything done to it and then when he took it that morning to get the oil change. Also when I test drove it nothing.

Here is my plan, before i'm going to throw it back on the dyno and get retune, I want to try somethings out. like if something got dirty from sitting.
I did put some fuel line/injector cleaner in, but haven't ran it long enough for it to go all through the system.
-put new IAC on. (311-420 is sending me one Thank you)
-check the TPS to see if it needs replaced or adj.
-change the in line fuel filter
-new spark plugs
-check coil pack

Anything else yall can think of.

just side note, when going through the gears to get up to speed it acts fine, at wot it feels solid, it is just when holding a speed it starts to do it.

ASh