just changing the diff mount aint gonna solve ya problem m8 !!

its all about the full package , the biggest offenders are them fookin shit big fook off bushes on the front of the beam , if you put a bar on them you will find they will actually lift about and inch up and down - these need to go , full alluminium units are req in there , then we have the rear mount these too have masses of play, this also needs to be solid mounted , the GRPA unit was a full diff back plate with the solid mount cast into it with the 4 bolt holes up to the chassis

tramp/axle bounce is very undesirable, the grip you loose is massive , this needs to be sorted, the reason that you sometimes get this phenomenon is that either you have got enough grip on the road surface that the force(propulsion) has taken the easier option than sending the car forward , so hence the traction breaks and the wheels come off the ground, when you dont get it (at full chat) is because the wheel will be spinning on the tarmac , hence the force has another easy route (no road grip) hence the massive wheelspin!! ok so far ????

as for the coil over job , springs and valving are another major part in the prevention of this , if you have no other movement on the rear of the car , then its down to the shockers , what coil overs have you got ??
i would poss suggest that the springs are too soft , and the combination of the 'bump' part of the valving is very low allowing the force of teh spring to be overcome and the fact that this 'bump valving' isnt enough to stop the oil flowing through the valves hence you will get the tramp.

if you are talking about what i call 'road going' coil overs then these are really only marginally better than uprated shocker/spring setup all you get is adj ride height, these manufacturers have to keep the 'road' element of teh spring/valve combination for drivability !!

hth

mark