On last flight I had a total payload of 3,670 lbs with 1,020 lbs being luggage & freight and the balance being passengers. Is this enough to trigger that there are people on board?
Yes. 3670 + 1020 = 4690 / 220 = 21 passengers.
I should also tell you that I configured a passenger boarding ramp for the aircraft
You mean a jetway ? You cannot configure that. It's up to the scenery having a jetway or not.
The "Parking has a jetway" option in GSX is only to tell GSX (ONLY in 3rd party scenery with static jetway) that a jetway that GSX cannot otherwise detect is there, so it should not call a Passenger Bus and the mid/front stairs.
It is a parking with a jetway ? If yes, which kind ? Fake/Static, standard FSX or SODE ?
Even a catering truck shows up...a small van.
The catering van will appear whenever the plane service door height is less than 1.65 meters from ground, so it might be correct or not, depending on the airplane.
It would be more interesting to see if you had a Passenger Bus, instead. Which will come ONLY if the parking is NOT flagged to have a jetway. You can try setting it like this, even if there's is a jetway, just a a test.
If you ALSO have a passengers Van, then it's sure the problem is related in some way to the airplane loading, since the Passengers MiniVan is supposed to appear ONLY if the estimated number of passengers is LESS than 5, and the Passenger Shuttle will be used from 5 to 20 passengers. The large BUS, will instead appear over 20 passengers.