All three of my TC/truck combos over the last 15 years have been over the GVWR of the truck by 700 pounds, 1,200 pounds, and 1,700 pounds. They have not been over axle or tire ratings. I've enjoyed thousands of trouble free miles of travel. The sticker in the glove box assumes you have a 150 pound person in every seat position in the truck. That's why it's lower than the door sticker.
RVers seem to be the only truck using segment that worry so much about GVWR (for better or worse). Farmers, ranchers, hot-shot truckers, contractors, and TC owners routinely run their trucks over the GVWR as a matter of course. Last time I was loaded heavy with my 2005 Chevy dually work truck headed for a job site I decided to weigh the truck and trailer. I had about 12,600 pounds on the truck (GVWR is 11,400). It handled my flatbed with skid steer and attachments over several mountains to the job site and back multiple times. I've got 248,000 miles on the truck and most of it's life it has been over GVWR. It's been the most dependable, reliable vehicle I've ever owned.
300 pounds? Please.