I was chasing this issue for ages on 3 different cars. Could only trace it to my current one where it was a faulty tyre. The belt was coming away from tyre.

Any kind of vibration will have its natural harmonic, so only evident at a certain RPM range.

Tire balance will do exactly what you describe. If they are 12s, suspect the balance even though they been done twice. You can test this by switch front & back wheels and see if it improves.

For the driveshaft, just unbolt it and rotate 180 degrees and bolt back in.

Not always mate n yes if u have takin the tail shaft out from where it got originally balanced it should always go bak into that same place

not sure thought if it wasnt that it would be from 0kph right through
could it have anything to do with the way it was put back in?

Have the tyres got anythink inside them ull have to take tyre off rim to see could be water inside the tyre I sounds stupid but have seen it before mate also is ur tailshaft running true

hey, i have a pretty bad vibration in my ute between about 60-85kph its fine above and below these speeds its fine
i have had the wheels balanced and that made it slightly better but it is still pretty bad. i dont think its the drive shaft or diff because that would just be a constant thing (right?)
can anyone tell me something that it could be?

thanks jac