Karl, there's been a lot of comment on this forum about mpg while towing, but I'll add my two cents. I have a Ford F150 with the 3.5 ecoboost 6 cylinder engine. I'm towing an A213HW which is roughly about 250 lbs heavier than your A-frame. The truck normally gets somewhere between 17-21 mpg on the Hwy all by itself. When I add the camper, I've had as low as 14.6 and as high as 18.2. That's considerably better than the 8.1-9.2 I got when I was towing my 7,000 lb. Palomino Puma 230FBS 5th wheel with it. The bottom line(s) seem to me to be these: Apart from truck-related factors, towing mileage depends on these factors:
1. The wind. Is it blowing at you or pushing you from behind?
2. The terrain. Is it relatively flat, or hilly?
3. How do you drive? Pedal to the metal or slower?
4. Your towing mode. Are you using tow-haul mode or standard overdrive?
5. Payload. How much "stuff" are you hauling in the back of the truck?
Age-wise, I am tending toward the geezer end of things. I am most comfortable towing around 60-65 in overdrive, with cruise control if the terrain is flat. If it is not flat, then I'm using tow-haul. If I'm going 60mph, it also makes my wife very happy. Takes a little longer to get there, but I like to think I get there more relaxed! Happy camping!