I've never had platinum plugs last 60,000. Mine always needed regapping ~30k anyway.
Plugs and/or plug wire problems first show up when pulling out at lower revs.
Carbon buildup can be a *factor* here. I start the motor, pull a vacuum line and spray carb cleaner into the intake plenum while maintaining ~2000 rpm with my hand on the throttle. Then shut it off, spray a bunch in, and let it sit for a while.
Then grind and grind until she starts and do it again. Unlike in-the-tank cleaners, this actually gets the valves and valve area...
Mike