We have an 05 Horizon. We had some problems with the motorhome in the beginning but Winnebago stood behind their product and corrected them at no cost to us.
I have a 400HP Cummins engine. I get between 8 and 9 miles per gallon. I had a 350 HP Cummins before this and got 11 MPG after break-in. I wanted a 350 Hp when I got the 05 But the dealer only had the 400 HP in stock. I believe if you stay with the smaller Hp it helps the MPG. I had no problem with the way the 350 HP got around.