Losing pressure

Ok, the machine is a 16 hp vanguard mated to a ar pump, direct drive. I’ve lost about 400-500 psi, and possibly some flow.Unloader is working. The unit has 600 hours on it. One thing I’ve noticed is rpm on engine is about 3450 but under load (spraying trigger) it drops to 3300. Is that normal?
I’ve also replaced packings and valves at 350 hours. Just replaced fuel filter, and air filter on vanguard. No change, kinda stumped. Is it time for packings again?

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Try getting new tips. Tips wear out and that increase in size lowers pressure. Also, lots of hose reduces pressure.