400 lbs over a GVWR isn't that big of a deal. However a single gross scale weight doesn't tell the owner the most critical things such as being over the trucks GAWRs and in particular the trucks rawr/and those P tire load ratings.
The 7700 GVWR package has a 4050 rawr and probably P tires. As Rick says those P tire's load rating is reduced by dividing it by 1.10 or roughly 10 percent reduction per fed regs.
I would get a reweigh with separate front and rear axle weights. That way you know what is over and what is under. You sure don't want to over load those thin sidewall P tires.