We have 6 tractors with Allison 6 spd  autos. They have 4:17 rears with 395 hp. MP 7. These trucks are 7 years old and only have had some sensor problems with them. We had a jacked E9-500 V8 with a 12 spd. This truck pulled like a locomotive. This 395 with the Allison would make it look silly. Only downfall on some permit stuff could use more hp. in the hills. You eliminate drive line shock load. Startability in soft conditions is better/excellent and when slow to a stop the engine brake and the retard in the trans will bring you to a 10-15 mph before using the vehicle brakes. I think if anyone ever drove one you wouldn't have a excuse why you don't own one. Other than getting around the price.