Four times is very strange especially if you have changed the box several times. If the only parameter that is changing, is Tq, with no yaw kicks (SAS/AFCS off) and no engine parameter change, look closely at the Torquemeter indicating system. Had a very similar problem with a S61, changed both engines, gearbox and still the same. Turned out to be wiring of the Tq through an aftermarket HUMS system. If you have IIDS, it will be tougher.
