Maybe the posted 645# tongue weight is a misprint as it would truly be an unsafe towing scenario with a 8400# TT. Tongue weight ideally should be between 10%-15%, anything lower than 10% is subject to sway conditions that will worsen dramatically at higher speeds. At 12% tongue weight will come in at just over 1K# leaving just over 600# for everything else in your truck including passengers. Still doable, but very tight with what most of us carry in our tow vehicles above and beyond just passengers. It adds up real quick for us with firewood and what not in the bed of our truck. Available payload is always the main issue when talking about 1/2 ton tow vehicles.
The Solaire 317BHSK is also quite long which will not help towing dynamics when wind is blowing hard and traveling at highway speeds, an investment in a very high quality WD/SC hitch is paramount for keeping this TV/TT combo safely on the road. It will be a good workout for your Chevy 1500, but if you mostly intend to tow on flat terrain it will get you there, any substantial inclines or high elevation towing will only magnify this issue. The stated numbers just might work out on paper, but often is not the true picture of what to expect when hauling your rig down the road, it's really about towing comfort, and when a TV/TT combo is at it's limits it is bound to have an adverse affect.
