To keep my tranny happy and extend its life, i drive with O/D off anything below 55MPH or where there are lots of hills or lots of red lights. And while towing...Do not leave O/D on. Or you will regret it. I have over 176,000 miles on my stock trans and it shifts perfect. Also when i start slowing down (if above 55) i wait till i get down to 45 and turn o/d off.. Only mod ive done is the check valve delete. Also when i start up my truck i put it in Neutral to get the fluid pumping threw it and get it warm for atleast 3 mins.. Not sure how the newer trannies are designed but on the 46re the tranny pump does not run in Park..
The O/D Button is there for several reasons. Turn it off in city driving/while towing/in hilly area's/and while having to stop alot/= longer tranny life.
My O/D never see's below 55, i always put it in O/D myself once i get to 55...I hold it there at 55..Turn O/D on..Then i continue to accelerate.. Call be picky, but my tranny is still alive and well.