Diesel Gator 4X6 delays before shutting down

Howdy,

I have an old diesel 4x6 gator and when I turn the ignition switch off it continues to run for about 5 seconds and then shuts down.

Has done it ever since I brought it back to life, runs great otherwise.

I have swapped out the fuel cut off solenoid and relay with known good ones, still has same problem.

any help would be great,

Thanks

Kelly