2deuce,
Under the 'better safe than sorry' category. I use an additive called 'Pro Long' (no jokes folks). I use the engine additive, the transmission additive and the fuel additive. I also use the Pro Long spray when working on firearms as a gunsmith.
I travel 850 both ways to visit my parents. On a return trip, the cruise control in my Suburban stopped working in overdrive. I pulled over and checked the transmission. Everything looked OK.
I proceeded to drive home in drive (less mpg) at about 75 mph with the cruise working just fine. The next morning, after a long day on the road, I checked the tranny again. The top of the dipstick was rusted. "What the ...??"
I took it over and had my transmission guy look at it. He told me I had probably destroyed the high speed impellor and those parts floated throughout my transmission, causing problems. He then ask where was the tow truck that dropped me off? When explaining I drove it over, he was completely shocked.
A week later, after rebuilding and strengthing my tranny (700R4) to handle up to 700 hp, everything was back to normal. My mechanic said he was surprised there wasn't more damage. He gave me a handfull of high speed impellor that had ate itself.
That's JUST one of my stories. But I use it and Royal Purple products in every vehicle we own. That WILL include the deuce when I get one.