EGT lag in one cylinder after start

Thought I'd share how this issue was resolved for those that are interested.  The problem turned out to be a defective hydraulic valve lifter on the #2 intake valve.  Compression tests showed cylinder #2 was not holding pressure and a borescope revealed the #2 intake valve was not fully seating, leaving a small gap.  So I had the cylinder head removed and the valve train disassembled and inspected, which revealed the valve stem/guide/spring/seat were all fine and within spec.  That left the lifter as the primary suspect.  Since lifters are not serviceable I just replaced it, and after reassembly the engine ran perfectly.

I think what made this issue difficult to diagnose was that the lifter didn't fail in the typical way, i.e., leaking oil and getting soft.  Several lifter checks showed this lifter was solid, not soft.  Instead we suspect it had a defective internal check valve that didn't drain oil properly.  This left the lifter stiff and extended when cold, preventing the intake valve from fully closing until the engine warmed up and thermal expansion loosened things up.