2003 Kia Spectra Rough start, CEL with P0302 code

2003 Kia Spectra has a rough start about 50% of the time. Throws a CEL with P0302. Sometimes drives a little rough too.

Replaced all plugs. Replaced coil for Cyl #2. Dealer said fuel pressure was below spec. Replaced fuel pump and fuel filter. Still throwing P0302.

What should I try next? Fuel injector?
Is there some testing I can do to narrow the problem instead of buying expensive parts?

Thanks!