Hi, this is whisky6, this post is to let people know about a problem that my son had with his 2006 chevy with a duramax diesel with the allison transmission,he plugged the block heater in when it got down to about 20 degrees here in wa. state over several days,got a check engine light came on,then it started to shift really bad,took into the dealer they checked it out and out that the sensors on the and transmission were not the temature,so computor told the transmission not to shift because it was cold,the engine told copmputor that it was warm,so they were a little confused which caused the funky shifting,was told not to plug in block heater above 0 degrees,they are working on a program at GMC to to let let people use the block heater at higher temps,the dealer cleared the check engine light truck shifts alright now,thank,s whisky6