The TC in a C4 is much bigger and they were ran with the same HP that the SOHC 4.0, there is more surface area to dissipate heat. Your tow requirements are pretty tough for a small-engined, heavy to begin with, vehicle like Explorer. Surface area undoubtedly has a lot to do with heat dissipation, but the original idea of cooling TCs only with outside air was abandoned; it just wasn't that efficient. The reason is simply that liquid/liquid heat exchange involves higher specific heat coefficients, mainly. I like your idea of an indicator for TCC condition. I have toyed with disconnecting PCM control of the TCC to a manual, or even vehicle-speed switch, thereby leaving the TCC ALWAYS engaged, except for slow-down/stop conditions. Negatively, this would confound the PCM, and throw codes. Let the transmission down-shift bring about necessary torque, to hell with the fuel economy factor of the TCC. After all, we do OK with 5-speed manuals, w/o slush-coupling, no?
How hot can trans fluid get before it will cause damage. I have tried to find an answer to this question but can't? I do know that it will boil. Can't give you a definite number here, but I HAVE seen ENGINE OIL in big diesels running on dynamometer test stands exceed 280`, even as high as 300+`, but this was considered extreme. 'Course, the biggest consideration, after ruin of parts susceptible to high-temp. degrade, like clutch linings, bands, is the FLASH point of the fluid, or some component in it. Fire would be the final ruin! My gut guess in your case is that 220` will not quickly destroy any component in your trans., but will degrade the fluid beyond a doubt. I worked in an oil seal molding facility in which petroleum-based oil was used as the heat-transfer medium to heat molding presses running fluid temp 360`, so obviously, this was below boiling and flash points. imp