each test port has a specific area or set of functions it is connected to
if you go into the service manual and go to the repair procedures and navigate to Manifolds there are sections that deal with valve adjustments. Each explanation tells you which port to connect to during the function test you want to test pressures on and adjust if needed.
system relief connects to ports 1 and 2
Steer relief connects to port 2
lift relief connects to port 1

so yeah it sounds like somethings going on if port 1 is low
i wish the manual went into more detail about both ports and their relation to the drive system. I can call genie and talk to an engineer and see if they can shed any light on it.
I'll see what i can find out and get back soon.