Our first rig was an '85 Class C with a 460 (caburetor). What a turkey that was. Warped exhaust manifolds on both sides had to be removed and resurfaced only 4000 miles since the previous owner had them done. He paid $2800 but a local shop did mine for $1200. The side of the doghouse got hot enough, even through the carpet, to melt the soles on DW's sneakers. I've heard tales of manifolds glowing red-hot when climbing mountain passes at full throttle, but low speed.
We got about 6 mpg at sea level and only 4.5 at altitude. There's a lot of altitude around here. Our V-10 (presumably an '01 chassis build) has been trouble free. In our 32-footer it gets a consistent 7.5 mpg and it doesn't change with altitude.
