Auto gearbox "skids" when reving - Surf 3.0 diesel 1998 intercooled version

[Bobby Ewing]

Hello you beautiful people and thank you for taking the time to  read my post.

I have a Toyota Surf  3.0 Diesel automatic 1998 intercooled version, about 1,5 years ago, the radiator broke, so  water in the  gearbox  ive been told, the garage, changed the  oil within,  change the radiator (not original but new) and so i have been driving about a year,  some  1000 miles i think or less.and suddenly after about 2 hours drive, wanted to park, when  put it in reverse, it wouldnt go, but instead a squicking noise,  and the car was shaking too,  like struggeling  to move and pulling a heavy weight  like.then  put it in drive , didnt move,  again R: no move but the engine was reving. so  , we did a new oil change  about 6 litres,i dont think they have changed the oil in the torque converter though. but yes,  new filter too.

So drove about 2 hours, same again , this time  whiles driving, about  20 m/hour, wanted to overtake a car,  heard the enging reving , seen the dial going up  to  3.500 revs sort of, but  the car wont  drive any faster, it was like  skidding. checked  oil levels , all good, colour is nice a red/pink sort of,  Can anyone please help at all ?  ( ps, everytime  this  happenes, i stop the car, park it for  5 min,  then  start engine, it pulls like a train again,  and lately  after  about  5-10 min drive in the city or off road, same happenes again, its revs but  wont engage in pulling untill i stop the engine  for a few min.

Many thanks in advance.