Sounds like clutch judder to me, could be old flywheel and a new clutch or it just needs a new clutch - what's the mileage?
Other options are;
Axle tramp - not likely at low speed and low rev's (unless your Wasso as that V8 can make it shake
Worn rear gearbox mount - Should happen when cold as well though
UJ on prop worn - again should happen when cold and you get vibration at speed, feels like the wheels are out of balance.
So I'm back with the clutch plate being knackered or if it has a dual mass fly wheel (OEM/Standard) it could also be a broken spring in that, the heat will affect this more than any of the others.
Just my tuppence worth
Good luck, hope you get it sorted