Pulsating vibration above 60 ?

My Barracuda has a harmonic vibration over 60 mph (3000 rpms) that I can feel in my seat .
It is rythemic... but slight .

I have checked my angles and had driveline shop check them .
Same shop built driveline.
Axles are Mosers with Green bearings.
Springs and shocks are new.
No vibration revving engine in neutral.
Happens with both my drag radial and michelins ( different rpmsdue to size differance) .

Possible that Shop messsd up but he has been doing my stuff for 30 years.