Picking up bad vibrations

[vxrphantom]

When i'm in 5th gear motorway speed etc and accelating through or from 2500revs I get really bad deep note vibration/resonance but only at that engine speed in that gear. 6th will pull from 2000 through no probs and likewise for all lower gears. Had new gearbox less than 2months ago. Any ideas?

[Magic919]

Sounds like a faulty gearbox.