I had the same issue. I went to an engine repair shop that worked on tractors. I took the truck and hitch to their shop and they came out and torqued them for me. It took two guys pulling as hard as they could on the long handled torque wrench to get it to click. I decided that 300 ft/lbs equates to just about as hard as you can tighten a bolt.
Oh, no... 300 is still hand tool range. We have some hydraulic torque wrenches we use to tighten bolts north of 6000 ft*lbs. Much more than that, and you start using stretchers to generate the clamping force just because the tools get too big and unwieldy.