I owned a 1985 Chev P/U and took the tranny out after 5 years of towing in O/D. Same thing with a 1991 Suburban, twice. Then i read the owners manual and learned not to tow in O/D. My service manual for my G. Cherokee also recomende no O/D when towing as did my 2006 Liberty, needless to say, i will heed that warning. I think a lot has to do with the weight of the load and i think most people underestimate the amount of weight they are pulling after we load up our boats with extra batteries, gear, etc.