It could be the pump. It could be the unloader (which on your unit is probably built into the pump). It could be a worn nozzle.
Start by checking that the throttle adjustment on the engine is open fully. After that, try a few different nozzles to see if that alleviates the problem. There is more likely a pump issue. I'm gona guess that replacing the pump on a unit like that is going to cost you almost as much as you paid for the machine new.
I know it's not a worn nozzle, as it's only got a few hours on it, but now that you mention it, It struck me like the motor wasn't running at the RPM's it should, if I remember correctly.
Also, although it wasn't building up to the pressure I expected, each time I closed the nozzle, it would build up additional pressure, and when I opened the nozzle again, it would spray at the pressure it should have, but only for a second or so, then drop down to the lower pressure.
I'm guessing you're right about the engine speed.
Since it sat for so long without being used, enough time for the choke mechanism to rust up, it may be it needs a little tweaking to get the RPM's up where they should be.
I also have a Ryobi electric pressure washer, that gets up to 2100 lbs as well,(same as the other) But the wand went south after about an hour of use.
The incredible thing is that I can find absolutely nothing anywhere on the internet. I'm guessing it's a discontinued model, but still, it's amazing to me that that particular model does not show up anywhere!