gas versus diesel 13.8 max weight fifth wheel

I can say from experience - get the diesel DRW. When we first purchased our FW, we had a 1999 F250, short bed, SRW, 6.8L gas with the 4.1 rear axle, 4WD. We got 7mpg and it stopped at every gas station. Stability was bad and towing up and down our mountains here was a white knuckle haul. We even had air bags installed and blew the lines on our first trip, and twice on our second. That was a clue that the FW was too heavy. Fully loaded with water full, we are about 14k (I know the exact number, just don't have that in front of me). Fast forward a year to when we purchased our current vehicle. WOW! Should've done it sooner DH says all the time. We have power to haul up and down mountains and stability is amazing. We joke that something is following us. The difference is night and day and in safety as well. Yes, diesel is more, but we also average 12mpg towing. Can't beat that. Now, ours is not a daily driver, but it was for DH for a couple of years till he purchased a sedan for our business. But, as a diesel, it will last and last. If you can afford it, do it. Both you and your main passenger will never regret it and we only tow about six times a year, if that, since we are both still working full time.