Land Rover Forum - Dead Disco, wont stay cranked.

Hi everyone,
Need your kind help. Own a Disco 2 with 164K miles. Stopped to get gas, after purchasing the gas cranked, engine turned but wouldn't fire. After about 10 mins fired and I drove off. Next day, she shut down while idling at a red light. Re-started after 10 mins drove home (after becoming very religious and praying a lot). Like a fool (thinking I could fix her) I replaced the Fuel Pump, a $400 gamble. Didn't work. She cranks first attempt (hooked up to a battery charger) but shuts down in Park after 10 mins. Odd knocking from a box under the driver side seat in the undercarriage (think this box had something to do with air suspension that has since been replaced by big red springs!) that quietly knocks intermittently at all times of the day/night. Have checked all fuses, relays time and time again. No joy. I am now contemplating replacing the crank shaft sensor as that seems to be the next most common potential fix.
Should I sell/trade her? I think she's got a good few miles in her if I can get her back to running consistently. All and any help/suggestions very gratefully received.