Given all the work you have done I sure would like to think you truly have the correct fuel pressure. Isn't the spec 41-46psi, or am I reading the wrong section of the Helms manual. Or maybe 98 has a different spec than in my 99 manual. If not, 38 is not that far from 41psi and well within a possible gauge error.

What have you done to check for an individual injector problem? Could it be you have a partial plug in one that is causing the problem?

Per the manual water and or alcohol in the fuel can also cause your codes. Presumably a water problem would have gone away by now. Any chance that fuel in your area went to a very high alcohol content for the winter? If so you might try a different brand or some from an outlying area. Granted this is grasping at straws but then again it won't cost you much to try some different gas.

Good luck.