There is a number on every tip (unless its been worn off!) that would read something like: 25040 - 25 degree spray angle and a 4.0 orifice. A 3000 psi/8 gpm machine would need 9.0 tips. (A 25 deg tip would read 25090.) If you are running a bigger nozzle 12.0 or 15.0 or even 30.0, it will lower your pressure.
Is it possible that your unloader has been adjusted in to lower the psi/gpm? If so, using a 4.0 tip would "feel" right, but when you put a 9.0 tip on, it would seem to lose pressure. Have you put a gage on it?
TIP: Use larger nozzles (orifice size) to reduce pressure at the tip without reducing flow. Adjusting at the unloader will reduce both.
