Truck cranks but won't start.

1995 F-250 7.3L with about 250,000 miles on it.
The truck quit quite suddenly. Was working fine drove it home parked it and now no start.
It cranks but it will not start.
It starts with started fluid and will run fine after that.
New fuel filter
I have checked the glow plug relay. It is working fine, I still don't think that it is the glow plugs cause after running the engine for 15 min. The block should be hot enough to start without them.
Any advice!