2008 F350 6.4 died on hwy, 70k miles

A few weeks ago, my truck died at a stop light and wouldn't restart. Looked at fuel filters because ignition seemed to work and seemed like a fuel system problem. Drained fuel filters, a little water, replaced filters. Still won't start. Bled air out of system. Mechanics hooked it up to Ford computer, no codes. Took out 2 glow plugs, said the two injectors for those cylinders did not spray. Hooked up a new one, and it worked. Today they told me they are thinking contaminated fuel. No warranty if that is the problem, and $6200 bill. Will take any and all thoughts as my day has just been ruined.

Thanks.