This is For "allison man" ... Allison Transmission

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.
This is For "allison man" ... Allison Transmission

Have you checked the fan clutch. I owned a GMC 1-ton crewcab and found that the noise such as you described came from a worn fan clutch. It sounded like the engine was going to come through the dashboard or blow up. Had nothing to do with the trans or the engine.
This is For "allison man" ... Allison Transmission

Took the truck to dealer mechanic and they said that this normal due to the fact that the engine was operating in "cold mode"