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A few weeks ago I went on the dyno for a tune and at around 4500-5000RPM the numbers would drop drastically. When it happened it would sounds like a bog/misfire but the tuner insisted it wasn’t a misfire because all of the numbers looked normal. We managed to get a couple good runs but most of the runs it bogged. I’ll include the graph with one normal run and one bad run.
While I was home trying to figure out the issue, I figured it sounds and feels like a misfire so might as well swap out the plugs so I replaced my TR5s with TR6s. Took the car out for a spin and it felt WAY faster and no bogging. I thought I fixed it but after a couple hundred miles it’s starting to hesitate a bit. Could it be just that he wasn’t able to tune it properly because the plugs were bad and I just need to go back with fresh plugs or is it something else?
If it felt better on a fresh set of plugs sounds like it was the plugs. Put in a fresh set right before tuning and take it straight there. Inspect the ones you just put in closely and try to figure out why it got so much better with a fresh set. Look to see if they are fouled from fuel or oil or anything else that sticks out as... bad
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What do you think happened on the dyno? 
