Allison transmissions and cold weather help

I've got a T370 with an Allison 2500 HS auto in it. Lately here it's been extremely cold at night ( sub-zero) and it takes quite a while in the morning to get the tranny to shift into drive. It'll shift into Reverse, but not D until engine has warmed at least 25-30 mins. I'm thinking this is normal as the tranny fluid warms up, but just wanted to run past those who are more familiar with the Allisons. The manual says nothing about cold weather operation. Thanks.

 

The truck is new, and is now back into the dealer after not wanting to go into drive this morning. Techs say it's definitely not normal. I had to tap on the electric actuator alongside the tranny with a hammer to get it to go into gear. Gotta love brand new trucks and the glitches that come with them!