Others posted in response last night to your other mentions of this to suggest possible torque converter problems.
I have a vibration at 115km (on the GPS rather than the speedo) but no problem changing gears and mine is the 5 spd not the 4. I changed tyres, rims, brakes and my whole suspension. I also got multiple wheel alignments and balances and had the ECU reflashed. I had a mechanic drive it on the freeway with logging software on the engine to rule out any mechanical issues there. Still no solution found.
Actually I see that yours keeps getting worse as you get quicker which is different to mine - mine disappears at higher speeds, say after 120 (not that I do that speed often enough to keep track of the precise cut off point).
Where are you located? We might be able to point you to a more effective dealer?
Also try this thread:
http://www.newtriton.net/phpbb/viewtopic.php?f=37&t=7328&p=131943&hilit=vibration#p131943
The Hitchhiker's
guide to the the Triton universe and NTN.
A how to on finding your own way -
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The two threads I wish people would use more:
thing 1 and
thing 2.