1988 Ford F350 Ran out of Diesel? Can't start up again--

(Before people start replying withh "throw that P.O.S. Away" I should say that the 14ft. Box in the back is painted with some incredible artwork, so I need to keep this truck running.)

So here's the facts:

1) Fuel guage is broken, and I'm afraid I've run the truck out of fuel a few times now.

2) This time I had fueled up rather recently, so either something else went out or somebody siphoned fuel out.

What I tried:

1) Put 5 gallons of fuel in
2) Took off engine cover and sprayed starter fluid as I turned the key.
3) Replaced batteries
4) Replaced starter (just happened to go out while we were trying to restart it)

Another note-- I DO have to spray starter fluid every morning to get the truck to run. I replaced all the glow plugs 4 months ago, but they still would not get the truck to start without the ether.

Thanks for the help-- if you'd like to email me directly-- its ArtistMoving@gmail. Com

thank you!
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Also, if the answer is to - check the glow plugs and replace if blown-- could you also tell me what else to fix so that I can start the truck normally and don't just blow them out again by starting with ether. I do make sure I turn the key on for 5-10 seconds before starting.