Automatic Transmission Problem?

the problem started gradually over 3 months..

however, most of the time, my 1993 Honda Civic with automatic transmission, would behave very well..

but tonight, my car couldn't go above 60km/hr (35 miles/hr) on D4.. i drove home on D3..

also, my reverse gear could hardly push the car backwards..

while driving on D4, the car engine would suddenly rev at high RPM but with little or no power to push backwards..

i can only describe it to be similar of having a car with manual transmission, and while driving on the road, someone would press the clutch puddle.. but again, my car has an automatic transmission..

i checked the transmission oil, it was within the normal level.. but my last tranny oil change was less then 7,000 km..

i want to fix the car at the nearest garage (about 200km away); but i hope i can have some idea of what it seems to be the problem