I'm the proud owner of a F250 diesel with airbags and the heaviest suspension available. I never realized what a bastard truck a 3/4 ton truck is. Most of the diesels have plenty of power to tow heavy loads, but they don't have the capability to deal with kingpin weights.
My Grand Design Reflection fifth wheel trailer weighs 11,092 lbs. dry, and I have a kingpin weight of just over 2K. My 3/4 ton diesel handles it, but it's about all I can handle.
I always think that a gas engine truck comparable to mine should hold off towing 10K. Sure, your terrain is flat for the most part. But the trailers you're looking at weigh too much for your gas engine.
If you're going to be towing with your truck, you might consider Grand Design's lighter fifth wheel trailers than the 337. Same goes with the Cedar Creek--too heavy.