Belt box for pump? Upgrade from DD to Belt drive

[fhpressurewashing]

You can find tons of info on here about people upgrading from DD to gear drive but I’ve never heard of someone going to belt drive. Seems like a much bigger PITA when the plan is to get a 8gpm anyway.

Upgrading my GX390 to 5.5 GPM... question

Have a direct drive 4GPM pump on it, going to a gear driven 5.5GPM. I’ve had this pump suggested to me: (Not buying from that site, just linking it for the pump specs.) It says 3500 PSI, but anytime someone talks about a 5.5 GPM, they usually say 2500 PSI. So what gives? Will the pump put out 3500 PSI with my GX390, or will it be down around 2500?