@223Wylde I haven’t read the full history here, and I’m unsure if you have auto tube order set, but I strongly suspect you don’t. If it’s not on auto tube order then negative airspeed’s rather then flipping the sign will be clamped at 0 m/s. So you can still be having problems or be wildly mis-calibrated but it would look like 0 m/s before you takeoff. Adjusting the offset by hand till you aren’t seeing spikes is an indication that you are moving into this region. Basically use caution as you preform that test as you might just be shifting values by more then expected till you encounter a serious problem.
5 m/s error in pressure reading on the ground would be an error of 0.7 m/s moving at 16 m/s, so the climb to 4 on the ground does not point at the source for the error of 4 in flight.