That poor of a mileage I would look for a leak as well, if the PO put in an aftermarket fuel pump it may be leaking by.
These are based on personal experience only.
The plug is on the left side just behind the battery, there is also a plugged hole you can put a socket in. @M61A1MECH do you make a plug and play harness for this?
I don't think you will have an issue; I have exceeded your passenger weight on a regular basis, with full saddle bags while pulling a 400-pound trailer.