One thing I have researched and did some leg work searching - I can't find or read about anyone (Healthy) & (Serviced Regularly) 68RFE driven by a civilized human being - under everyday driving or towing @ or below the advertised towing limit.

Failing due to below average operating temps - which these days seems to be around 185 -195*F.
When I was growing up and learning from Dad & Uncles, it was 170 -175*F was a limit - I guess today's higher quality ATF plays a part in this matter.
Or Possibly todays Manufactures - don't care as much about their designed & built creations lasting very long - You can't make & keep profits up if your products last much past the warranty period.

To this day, this modification is the Most Effective Mod to date that I have done.
During the winter months - I watch all my temps (when first starting and driving off) - I always start slow & gradually work into it - until the Coolant reaches - 170*F / Oil - 145*F / ATF - 75/85*F Temps. (Before I ever go over 60-65mph)