Pete 587 isx15 acceleration issue

[Alexp86]

When I lightly press on the accelerator it doesnt move, but if I hold it there or push it down further it seems like it catches on and accelerates really fast. Any idea what may cause this issue? Im about to buy a throttle sensor, but not sure if that'll be the issue.

Also it has been jumping when i put it in gear or accelerate from a stop, if it stays in 2nd gear it keep doing it until I hit 5th or 6th then itll stop jumping when it get back down to 2 its like it resets. It only happens every once in a while sometimes itll got 1000 miles without doing it.
when it jumps its very hard makes everything in my cab fly around could that be caused by the throttle?
I did replace all my batteries a month ago and it stopped for 3 weeks but that couldve been just a coincidence cause like i said sometimes it will go a while without doing it.
I did have some trans issues where it wouldnt go into gear, but ended up having the dealer replace clutch and actuator cause they said my inertia brake was broken, but before they did that I was having issues on the road and took it to a shop where the guy didint seem to know what he was doing. He said the software needed to be updated and when he was looking through his eaton software he was like ummm i wasnt sure what version so i chose the generic.... ever since then it started with the jumping also my gears seem to change sooner than it used to ill be on like 6th or 7 by 20mph.

Any help will be appreciated.