I'm having the same trouble with my 6.3 right now, though it turns over just won't start until it cools down. The shop manual has a troubleshooting guide / procedure taking you through fuel pressure verification once the electric pump is verified as getting 11-12V, as well as MFI linkage operation verification.

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Francis E. Abate
Automotive Restoration & Preservation
Sheet metal, trim and upholstery