Reducing jitter and improving speed of accelerometer output
It sounds like the display response time you need is fairly and squarely coincident with some of the dominant vibration frequencies seen on the tractor's front loader and this could be a right royal b*tch to solve. In my opinion you do need to sample at a much higher rate to prevent aliasing - this is high frequency vibrations becoming aliased down to lower frequencies due to inadequate sampling rate. This may be enough to overcome your problem. Next is higher order low pass filtering like 2nd order of third/fourth order. It seems, in your question you have implemented a 1st order filter but this could produce much better results at a higher order BUT, you're running out of CPU speed.

OK, as a definite must-do thing, you must remove frequencies that can cause aliasing at your sample rate and maybe consider a fourth order analogue low-pass filter by cascading two sallen-key filter stages. Here is a calculator that you can set for a low pass frequency of 2Hz (the best you're going to get with 10Hz sampling and lots of nasty high frequency stuff.

Good luck - I'm not going to say you will be successful without some form of mechanical dampening and a high order analogue LPF at the front-end.