Sounds like TC Clutch slippage to me. Have you checked your fluid? Let us know what the level reads and the condition of the fluid.
You could try to get it scanned, but if there is no CEL on, it possible will not pick up anything. I am not sure if slips are always kept in memory, but I know that my TC clutch slip was.
If all else fails, you could always go and get a bottle of the Lucas Trans Fix, but it will not help if the pump has went under.
