Steering head bearings, checked those handlebar mounting rubbers?

are the wheels in alignment?

I'd recheck the balancing too

just done all that.. i replaced the front wheel bearings just in case and i also changes the fork oils seals. i did notice the yellow dot on the rear tyre was not lined up so i reseated that... it has got better tho and it only has a slight wobble now when I'm traveling at 70..

its slightly better because you reseated the tyre?

as far as i know the yellow dot doesn't have to be lined up with the valve, as long as its balanced properly.... where the dot is shouldn't make a difference.

it usually means less weights on your wheel if its lined up though.....

Are the spokes tight? tapping them with a spanner is a good way to check, if you get a nice ringing sound it is tight, if its a dull thud then you have a loose spoke. (do them one at a time)

+1 on checking the spokes and also checking the wheels are true.

On a different tack for a second.

Do you have panniers?

Are you bigger than average Joe, not just weight broad shoulders can do it.

Are you relaxed on the bike, too tight a grip can cause shimmy.