What are some signs that I should be aware of so I can know when an auto transmission is starting to slip?

Signs to be alert to that could indicate a slipped transmission are leaking Transmission Fluid and whining engine noise. If your RPM gauge exceeds 3500, that's a clear sign. If the car won't accelerate quickly, or coasts for a long time with your foot off the accelerator, those are signs.

Your accelerator vibrates or produces an acrid smell. Tour car may also pause when put into reverse. You are in big danger when the accelerator is pushed, the engine revs up, but it doesn't move.