I think you have other problems. I never had that kind of response in the same temps at the same speeds with a non lockup converter. Are you running throught the radiator and the air/oil coolers? Add that I was running at those speeds, then suddenly sitting still in ATL rush hour traffic, then running those speeds (and higher) again, up and down the local hills and dales, and pulling a trailer with a load. The only time I lit the lights was 4wdhi grunting at low speeds on extreme climbs in very hot weather, way down in the rpm range with almost no air over the cooler/radiator (the engine coolant was getting hot, too).

I'd be flushing my cooler/lines.