Bought demandated isx, issues tune related??

[BarelyAbleFarms]

So I purchased a 07 9400 with a isx that was demandated. The neighbor claimed to have the tools and have connections to tune it. So I took a chance with him. 4k later the truck still has all the issues it had before. Let me break down what I'm experiencing.

Rough starts, warm and cold

Very jerky throttle through all the gears. Impossible to drive smoothly. But sitting still is seems to rev up smoothly.

Inconsistent rev governor. 16k, thru 19k randomly. Cruise does the same

All this makes it very difficult to drive, and I'd rather drive anything but this truck.

What ive tried, new speedo sensor. New throttle sensor. New back pressure sensor. New boost and barometric sensor. Or whatever it's called.

The only code my scanner comes up with is exhaust back pressure sensor erratic, incorrect. Pid131fm12

I'm really curious if anyone has an idea where to look. Or if someone a quality time could fix. And if so, who would be recommended to get the tuning from.

Thanks in advance for the help.