just bought 85 K-20 6.2L diesel

[Ozark Tim]

Just bought this truck.
Has 139k miles on the truck.
Runs good but after it sits for 3 or 4 hours or overnight when you start it, it will start and die immediately and then you have to crank it and bleed a knob on the rectangular box on the firewall then do again a few times and it will start and run fine after the 3rd time. Leak in a fuel line?
Anyone ever dealt with this issue?
Nice truck and planning to use it on the farm but dont want to have to bleed it every time it sits for a night etc.