I'm glad to see so many "weight police" trying to explain this to him so it isn't just me.
A 3/4 ton truck has something like 1700 pounds of payload. I don't care what you do to it, putting 4000 pounds on a truck like that will never be safe. Maybe nothing bad will ever happen, but that doesn't mean that living life on the edge is safe. It's your truck and your choice.
One day the government probably will crack down harder on people who overload their trucks like that. But it's going to take some high profile incidents first.