Okay.....sounds like MOI settings need some adjustment. I copied a set of MOI data from a plane to show you what is what and how to adjust them.
empty_weight_pitch_MOI = 278670 <<lower this number to fix up/down shakes
empty_weight_roll_MOI = 109624 <<lower this number to fix rolling
empty_weight_yaw_MOI = 279527 <<lower this number to fix side to side shakes
The stronger the shake, the larger the reduction needs to be to correct the problem. For severe shaking, reduce the number by 50%. For medium shakes, reduce by 30%. For minor shakes, reduce by 20%. If the shakes continue, reduce by an additional 5 to 10% of the original value until the go away.
Be aware, that changing these number to correct flight behavior can cause new issues with ground handling. I would trade taxi stability for flight stability any day of the week.
DSICLAIMER: I am not a flight dynamics guru. I know just enough about flight dynamics to be dangerous and/or really annoying. Use the information above at your own risk.
Always make a back up of the stock config file before you start following my advice...that way if what I suggest blows your plane up, you will have a working config file to put back into place and use until someone who actually knows something comes along.
OBIO