Agree that jolting is 100 percent the JB4. I can’t speak for other piggybacks since this is the one I have. I can’t speak about the ecu tunes either but I beleive
@Tonkabob does not get that jolting but he has an ecu tune. I have personally tested their numerous times. I beleive I have posted about this complain on other threads as well. When I have the JB4 off the car shifts smooth, when JB4 is on the car on map 2 I really feel the jerking in between shifts. It more noticible when taking off from a dig between 1-2 and 2-3.