My best suggestion is to be an informed buyer prior to going to the RV Shows.
Anytime you get a bunch of competing dealers together, the egos arrive and the prices can come down. But only doing your homework first will let you know what's a fair deal.
As far as any single rear wheel pickup hauling any fifth wheel trailer, your weakness is going to be the Kingpin weight. When Grand Design trailers arrive, the posted pin weight's going to be substantially more.
I limited myself to a fifth wheel trailer weight 1600 lbs. less than my 3/4 ton diesel truck can handle. The actual pin weight is within 400 lbs. of my maximum rated limits. I'm max'd out. You might want to consider a trailer slightly lighter than the 320X if you're not going with a dual rear wheel 1 ton.