I thought that this was a 2.2 . the 4.3 I did not see much about head issues.
with the chk eng Lt I would also guess its a mis fire . remove plugs compare. could be a cracked spark plug damaged plug wire plug wire routed wrong not properly secured and got melted/short.
using a ohm meter measure the wire resistance they should all be the same or close to the same resistance.
if a plug looks different from the others then check compression compare all should be close.
with the headgasket the O2 does get damaged if your gasket issue allowed coolant to be injested by the engine. also the O2 could be the original. these usually last 10 yrs/100,ooomi. some get more than 100,ooomi with mostly hwy driving.