cyclic drivetrain vibration

Too many possibilities, when you say 3rd gear 45-55 is that with TCC on off or both?
When in OD 70-75 TCC on off or both?
Drive angle corrected, what is it set at?
Sounds like RPM or driveline speed related. Can you duplicate at a stop slightly raising RPM"s
in park or neutral and then in gear power braking bringing RPM" up into range, let us know