"Houston, We have a Problem" Help!

Hello, everybody
I have a 93 with 110K on the original tranny. Tranny has external filter, cooler, and temp gauge. This weekend I drove on the Interstate for 150 miles one day and back 150 miles the next day. After warm up, the tranny temp gauge stayed between 155-170. After everything had warmed up, I would occasionally be aware of a "stumble" somewhere in the engine or tranny. Then later, while cruising at 65-70 mph, something would happen to make the tach momentarily "flare" from about 2300 rpm's to around 3000 rpm's and then immediately back, as if the torque converter had unlocked and then re-locked. This would happen several times in succession. Then everything would be fine for another 10-40 miles, until the next episode of several of the rpm flares. It did this periodically on both days of this trip. To my amazement, it went up a rather large mountain at about 65 mph without incident.
This may be only a coincidence, but the dash light array that lights up to indicate what gear the tranny is in lights in every gear except "D".
If anyone has had these symptoms or knows what's going on and what to do to have it fixed, please reply. I hope I've supplied enough information. If not, please ask. Thank you very much.