You could have a plug end problem as stated. Reducing firing voltages by replacing plugs can cover up such problems.
Leaving your car idling (probably with A/C on) on a summer Florida day for extended times is a definite stress test. you stressed it and it suddenly broke, seems logical to me.
BTW, why haven't you replaced your valve guide seals and dealt with the oil and spark plug consumption?
Bosch Master, ASE Master, L1
33 years MB technician