You can look up a VIN Decoder and verify the Model Year. There's probably also a Transmission Code on the door jamb label. Also, Shift Knob on 4-speed (4R100) is marked "OD Off" and the 5-speed (5R110) says "Tow Haul", or "T/H" or the like. The 2005's probably started build in AUG/SEP 2004.
Drive this coach and WEIGH IT!!! Find out what the Wheelbase and Actual Coach Length are. Some of the "Guides" say WB/Length should be at least 52% for good handling and tracking on the road. I believe it should be in the upper 50%'s, closer to 60% the better.
Weight (at a truck stop CAT scale or the like) will tell you if
1. Front Axle bears enough weight for good tracking and
2. That the Rear Axle is not overloaded