[jclark003]

A dead cylinder can certainly result in a lazy engine unable to hit max rpm. However it's hard for me to see it causing a roll back in RPM on the top end or a bouncing tach unless there are multiple issues with that engine (entirely possible).

Without a compression test done I'm not sure how your mechanic diagnosed a dead hole much less concluded a complete rebuild. Also poor compression often relates to valve issues rather than piston problems and pulling one head isn't nearly as involved as a major overhaul.

ive seen a lot of seemingly large problems be the result of something small and cheap. Make sure you throw a set of plugs and wires at it as previous posts have suggested and then go from there. Swap parts with your good engine if you aren't sure and want to test things. Definitely compression test the engine before going inside.

Best of luck and keep us informed.