I have got a TR 92 model and recently i have noticed a few things
it is an auto by the way

1. At idle and NOT in gear the car idols fine, but put it into drive that revs drop to 400-500 and the whole car shakes not alot but noticable. When the car is in motion it is fine no problems any ideas

2. When the car is driving the grearbox slips?? out and into to netural and I would have to let the revs drop for the gearbox to pickup again, this appears to do this about the 3500 to 4500 rev range ??? but the problem is that some times when this happens the gear box will only pick up 3rd gear and will not drop out of it.. I have also noticed that if I turn the engine of and restart it it goes away and the car starts of in 1st again

Any ideas i think the clutch is going ???
Thanks

sounds like the clutch things in the box going... most common prob with autos along with bearings going. mines doing that too.

I, too, until recently had the same problem as you describe.. the problem was with my auto (91 TR) was like this:
a) had the same idling issues in drive
b) was slipping into and out of nuetral often
c) was staying in 3rd most of the time
d) after turning off and on it went back to first - next time it happens just out of curiousity try just jiggling the key to the right whilst your driving, but not so much as to make that horrible grinding noise - you will find it changes to third - like mine did

how i fixed the prob - new gearbox or reco unfortunately.. what happened to mine was that i lost second gear as well as overdrive. (every time i tried to put into OD, it just revved into nuetral) so I had only really first then straight into third.. it sucked

for the price of a reco - (was quoted various - from 800 to 1500) i decided against it a got a replacement box for $880 with 6 month waranty.

sounds like yours is doing similair - sorry to give you bad news but id say its new box for you mate, best take it to someone who knows - the guy i took it too drove it around the block and knew straight away. ( which was magnawreck in currumbin, gold coast ) good luck - hope ive helped