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98 5.7 Silverado miss under load or uphill

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Anyone please feel free to point me in an area I have not been. I have a 98 Silverado 5.7 that misses and skips going up a hill under load or if you get halfway up the hill, back off the pedal and then gently press the gas pedal again to resume. I have had the fuel pump replaced within the last year, put a new filter in today. Idle PSI is 53, while driving under the failing condition it is around 58 PSI. The injectors were changed to the MFI from CSFI last December. The plugs. wires, rotor button, dist cap and coil have been replaced. MPG is 16 city. around 19.5 on the Hwy. If the hill is step and long enough I get the generic P0300, random misfire code. The condition is starting to get worse ( easier to produce the failure ) so I need to get busy. Thanks for any Ideas. :think:
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I am not sure about that 5.7, but on my '99 5.3 I have broken my wiring harness about 3 times. Which causes it to miss. Might try to check that. Take it to a dealer and they can tell you exactly which cylinder is messed up. Then you can go from there.
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