I did a search of the forum and it seems I can't find anyone with a similar issue.
Cars on 130K miles, just fitted 3 new engine mounts (front, back, engine top mount), gearbox mount doesnt seem to worn (although this may infact be my problem), other three were completely shot. Problem was there before and after the 3 new mounts, potentially maybe slightly worse after new mounts but marginal.
The problem only seems to occur when you plant your right foot flat to the floor between 60-73mph in 6th gear under heavy load which is between 3,000RPM and ~3,600 RPM which is the exact speed I like to drive on the motorway. The engine seems to vibrate the dash and through the steering wheel, then the vibrations dissapear after that speed and stay gone. Also this only seems to happen in 6th gear, while I tried to simulated this is 5th, 4th, or 3rd I cant get the same vibration under load at those RPM's that I do in 6th...
I swapped wheels front to back, no change, and they have been checked for balance and they are fine. Obviously I replaced the 3 engine mounts I listed above which made a huge difference to the feel of the car, clearly the engine is not vibrating all over the place, gear changes are better, engine rock at idle or slow speeds is massively reduced, etc... but I still have this vibration under load issue. To note, with the new engine mounts there is a slight high pitch vibration at idle, but I guess that is normal as is probably like fitting es mounts to older mounts, like some describe on the forums!
Does anyone have any ideas, or any other tests I can do to try and narrow the problem down a little more? At the moment Im thinking its drivesahft, maybe half shalf bearing or gearbox mount related but I cant be sure. Further Im sure my rack slider needs replacing as it hasn't been done in 130K miles so ill be doing that shortly too.
Thanks for the help, really appreciate it!
Thanks, Matt