have a 1997 silverado k1500 4x4 5.7 it was showing po155 o2 sensor heater circuit and po 306 misfire cylinder#6 did comlete tune up compresion test showed 150 in cylinder still mis and service engine light still flashes.the truck ran perfect went through a rain storm shut it off next morning it was throwing these codes and hardly run.

Have you replaced the bad O2 sensor? Newer sensors have a preheting element and if they don't reach temp fast enough it is detected by the ecu.

Yes

I suspect the Ignition Control Module (ICM) is failing--$83.00 at AutoZone (DR178). I would also replace the coil (C1098, $40). Easy 10 minute job. I recommend replacing these problematic components every 120,000 miles or 10 years, whichever comes first. Otherwise, they will leave you stranded. Apply dielectric grease to connections. Make sure you only use ACDelco platinum plugs (gapped to spec), with the same part no. that originally came in the truck. Apply a light coat of dielectric grease to the porcelein portion of the plug, as well as the top electrode. This will help prevent misfires.

This link should help:

https://www.askmehelpdesk.com/cars-t...ml#post2028083