my engine loses 2-300 rpm when kicked in to passing gear. on 2003 Chevrolet Silverado 2500 HD

I have replaced the rubber fuel lines. the check engine light came on but went off before I could read the codes.

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2 answers
Codes are still there, unless you have removed the battery cables for some reason. Computer has a good memory!
Turbo working?
scan codes and post so we can adv