67 on those mountain twisties sounds bad enough, let alone adding 5k worth of trailer behind. If your tires are rated for the speed they'll handle it, but I'd still slow down if I were you.
Aside from the aero help, that diesel will thank you big time if you keep the RPMs down a bit.
Edit to add: the "truck" speed limits only apply to commercial vehicles, a 3/4 or even one ton pickup is not a truck, no matter how auto companies like to advertise and sound tough.
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