I let the truck idle for about three minute in neutral before pulling out. However until I drive about 8 miles the noise coming from under the hood or truck drowns out the diesel engine sound usually heard. The sound is like a huge fan turning or like the trans. is being over spun or like it is being worked very hard. The truck also shows weak accelleration during this period similar to when one is towing 8000+ pounds. Any ideas what this could be a symtom of? Is this normal operation for the Allison? The truck has about 600 miles on it. It has been acting like this for the last 160 or so. Thank you for any replies.