We have a 2003 Dolphin on a W-22 with 8.1 and Allison with 94,000 that we ordered from factory and took possession in the fall of 2002. From Kansas it has made several trips to NM and Phoenix, 3 trips to West coast and a 10,000 mile round trip to Alaska up and back thru BC not the 4 lane in Alberta. Most of these trips have been towing a 1999 Grand Cherokee. We have had no issues with the engine/transmission. I have always used synthetic oil and had Allison change out the original transmission fluid with Transynd synthetic at my second engine oil change.
With all of this it still only uses about 1/2 qt. per 1000 miles. I am planning (hoping) it will go another 100,000 because we really like our coach and don't want to have to replace it.
I have been pretty religious about routine maintenance, and before we left for Alaska with an 11 year old coach I replaced all rubber components in the engine bay - plug wires, belts, and hoses, including any rubber fuel lines. I also run mid grade fuel whenever I am towing to prevent any pre-ignition knock. But when traveling without the toad I just run regular unleaded.
