Drivetrain vibration problem

I have a drive train vibration atm, and Im trying to isolate whether its a Uni, pinion angle or an unbalanced drive shaft.

My pinion angle seems to check out within spec - at least as per Dr DIffs recommendation - but I have the following problem -

1/ The drivetrain vibrates quite heavily at low speed, either coasting down at slow speed to the stop lights - travelling at a constant 20 mph, or accelerating from a standstill.

2/ The vibration decreases significantly at around 45 mph, and returns at a much higher frequency at around 55 mph.

3/ The vibration does not magnify when I lift off the throttle at high speeds. (So the pinion dropping doesn't make the problem worse)

I have changed the rear uni but it had little effect.

Just wondering if you think its more likely to be a front uni (which doesn't feel worn at all) or a pinion angle problem, or a drive shaft issue?

Happy Easter to you and yours....