Bought our first 5th wheel in Sep '04 and after a ton of research ended up with an '04 F-250 PSD. The decision maker is whether or not you intend to do any appreciable amount of towing in the mountains and or crossing any of the 12k foot passes. That's where the diesel shows it's stuff.
One thing you have to watch very closely is the pin weight on the 5th wheels. You can get over real quick on the 250/2500's. After many trial and error trips I found that I needed to carry about 20 gals of fresh water to offset the overage on the pin. Think see-saw syndrome.
I just replaced the F-250 this week with a F-350 PSD. Now my problem is finding out what issues that I face with the F-350 regarding hitch height since the F-350 is about 5 inches higher with the 4x4.
Avvid...long bed weighs more, so you loose it in payload.
We too were just looking at a Ram 2500 (gas). I like the look and it was lower in price than most of the 1/2 tons. Patience....not buying for another year!
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Eddy & Brenda
Canton, OH
2015 Silverado HD 6.0L
2014 Zinger 32QB