1988 transmission strange noise and smoke

I have a 1988 with the AW-4 automatic. I was heading up a fairly steep pass with transmission in the power mode. I suddenly started to hear a whining noise similar to what a power steering pump sounds like with no fluid.
I then pulled over and lifted the hood. Puffs of smoke were coming out near the bell housing area. I looked at the fluid on the dipstick. I first saw nothing, and tried it again, and the level was ok.
I turned around and headed home. It now seems ok but then again, its not under the heavy load of the pass. Any input would be greatly appreciated.

Well, if the trans fluid overheats and/or is aerated you would get the whine similar to PS pump from the trans pump.

Type of fluid, how many miles/years on the fluid, what type of driving?

I am using Chevron dexron mercon. I do have about 30k on the fluid. I typically do drain down and partial refill. I have not done a full transfusion or ever dropped the pan. I use this as a daily driver and don't do very much towing.
Do you think I did any damage? I stopped and pulled over as soon as I heard it, then drove it home.

Interesting.

Slippage equals heat, heat reduces life of the transmission fluid. On a hard pull, slippage may be putting out too much heat for the fluid to handle at 30k. I would start there, do a poor man's flush on the transmission--search for Poor Man's Flush.

Sounds like a winner. I'll give that a try. Thanks for the sound advice joe_peters! Most appreciated.