A big thing I learned for us auto guys is to put it in neutral because it moves the fluid around and warms up the tranny too, but dosn't do it in park. Nolt sure how true that is but it can't hurt. I let the revs go to at least 1000 if I'm in a hurry, usually to normal idling if I'm not. But with the temps we get warming it up is a must if its -20 or more. I let it run for about 7 min once at this temp and it seemed ok so I drove very slowly and the engine was very slugish and the tranny came out of drive by its self because it was too cold. My trans is fine 8,000 miles later and was fine after I let if sit there for a min or 2. Just don't start it up and immediatly drive away unless you really want an escuse to do a 3L swap.
