That looks like probably the Red Lion brand. They're only rated for 2500 psi, but I haven't had problems using them on machinery run by a tractor running 2900 psi, but they're probably not working at full capacity either.
I wouldn't expect a catastrophic failure running it at 3000 psi, but blown seals, bent pistons, broken clevises are possible. I'd either set your relief valve at 2500 if it's adjustable, or at least plumb a pressure gauge in so you get an idea how hard it's working.