Is there a miss or does it just fall on its face? If miss pop the cap on the dizzy and see if the shaft has a lot of play in it. One of the telltale signs is the tips on trigger will be shinny because the are contacting the outer ring do to shaft slop. I've had a matchbox style distributor go bad this way, the miss started right around 4500.

I've never had a motor float the valves below 7500, I would think titanium springs would be race parts and the rate be high enough that even going south would still hit 6k.

My .02