I am one happy camper today. I hope this fix will help others with the same problem. When my '95 SLE got hot, usually after about 45 minutes of driving, the torque converter would not stay in lockup. As a result, at 65 mph the tach would jump from 1900 to 2800 rpm and stay there for the rest of whatever trip I was taking. The TC would not lock up again until everything had cooled down.
Not sayin' it will work for everyone, but I installed a Long (brand) low pressure drop, stacked plate transmission cooler, (willwren recommended the type) and now my trans stays in lockup even when the car is good and hot, and the AC and cruise are on. My oil pressure is even higher than it used to be, and I am still running my wintertime 195* thermostat. Everything must be running a little cooler. Boy, I wish I had installed this thing a lot sooner.
I did not buy the biggest unit, but the one rated at 13000 Btu. The design of this cooler eliminates the need for valves or thermostats for cold and hot weather, it controls flow by the viscosity of the oil. The unit is very well made. It cost me $56 delivered to my door with all the necessary fittings and tubing and took less than an hour to install. I mounted it right in front of the passenger side fan. Here is the link to the product: