MPG woes

Sounds bad. I get about that + or - 2 with our 30 ft. Class C V-10. But before you give up realize that the way we check MPG isn't real accurate and 1 short trip isn't enough to get close to a true reading. But, if you can't get 12 or 15, I guess why have a Class B?

That mpg doesn't surprise me. For the year and the rig. If your willing to travel at 50 mph you will probably gain a couple mpg.

I had a PW, it averaged 12-14 on the highway, normally 55-60 mph. Mine did not have the high top your picture shows. Around town was about 9-10. I agree with the statement, do about 3 fillups, average the 3. Also, if you were running generator, that figures into it

Other than driving slower there is not a whole lot you can do to vastly improve mpg. We tow our 32' TT and average about 8 mpg if we don't go over 65mph, unfortunately we tend to go a bit faster on the instates out here in the West. I stopped fretting about mpg early on when we starting RVing over a decade ago knowing it is just part of the cost to enjoy this lifestyle. Haven't recorded mpg on a trip in over ten years.

had 1998 looked almost like yours ,got 14teen all day long. we don,t drive over 65 mph. my 2007 LTV only gets 20mpg its a mercedes benz 5cyc diesel.

The wind drag is what does you in...

a friend of mine used to have a 1991,looked exact same as yours. got 14.3 mpg averaged over 1200 mile round trip. for what its worth.

Might try a bug deflector on the front of the hood. It may direct the air up over the top a little more efficiently.

It sounds a bit low to me.

We have the same engine, only with a carburetor and no computer. We get 8.4 towing, which according to others here is reasonable. Not towing it was somewhere around 14 - I checked years ago and never wanted to check again. :o We do travel at whatever the speed limit is though - no slowing down...

3 things affect mileage the most: aerodynamics, speed and gearing.

You can't do anything about the aerodynamics. Most trucks built back then were designed to run at the 55mph speed limit. However, engine speed will drastically affect fuel consumption.
Too slow causes lugging the motor, too fast puts the engine past peak power. Both conditions use fuel.
See if you can find out the rear gear ratio. It's possible the truck was built with a numerically low rear axle ratio, like 2:52 - 2:73. If so, the engine at 60 mph is running way too slow to use it's power and lugging the motor. That runs the throttle more open to keep speed up.
There are online calculators that will convert engine rpm, vehicle speed with tire size and give you the gear ratio.
For a heavy vehicle will poor aerodynamics a better ratio would be in the 3:30-3:50 range.