Mitsubishi has a fuel pressure test adapter. It sits between the firewall hard hose and the flex hose going to the engine. The test adapter has a schrader valve on it to attach an external fuel guage to it. I have one somewhere in the basement. If you want to use it, let me know and I'll try to dig it up.

Mitsu # 6 - 98 6G72 Montero Sport, Locking Rear Diff, Aisin Manual Hubs, 31x10.5

Mitsu # 7 - 02 6G74 Montero Limited