It would turn over but wouldn't stay cranked?

Hello,

It does sound like when you are on an incline the fuel pump is unable to pump fluid to the engine. It can happen even if you are partially empty. Just about when the pump in no longer submerged in fuel you can have this type of no start. There is a check valve inside the fuel pump, intend to keep fuel in the pump in case like this. But over time it will leak and there will be no fuel to start the engine. Typically if the vehicle has been siting for a long time this tends to happen.
This check valve is a part of the fuel pump assembly and to replace it you will have to replace the pump.

https://www.2carpros.com/articles/how-to-replace-an-electric-fuel-pump

I have attached diagrams for your reference.

Please let me know of any questions.
Thank you.