I have putting up with a miss that comes and goes. So far I have replaced all the relays, power stage, AMM, cap, rotor, wires, fixed bad wiring to the radio suppression relay, and replaced the coolant sensor. The motor only has 38K miles on it. My tech is looking at the possibility that I have a weak valve spring in the head. He is probably right but I still think it is electrical.
The reason I'm now looking at the Hall sensor that may be going down since there is just over 100K on the distributor. The second reason is it is temperature related. I had the coolant sensor replaced in Jan and had zero miss problem until this week. This week the temperatures headed into the 70's and the miss has come back after running the car for a few hours. Last night I took it out on the interstate and put it in third gear and set the cruise to 70 mph at 4200 rpms.
I figured if it was a bad valve spring or sticking valve it would show its ugly head. Well about 5 miles into my run the miss started again. I back the car down to 55 mph at 2000 rpms in OD and all was well for about 5 minutes. Back like a bad attitude the miss started up intermittently. What is annoying is it only happens once the care gets nice and hot. Around town there isn't a problem as long as your not running the car constantly for over 2 hours.

So guys I want to pick you brains on this one. What do you think it may be?
Thanks Al.

Coil? Or maybe a bad intake air temp sensor in the air filter box.

Nope on both. I checked the in box thermostat and it's A OK and last summer when I was trying to debug this miss I swapped in a old coil I had laying around and nothing changed. I had installed a new coil at 250K just because it had 250K on it. I was thinking last night that the FPR has about 50K on it. If it was acting up would this also cause a miss? One thing is it doesn't miss when accelerating. If it starts to miss and I push the pedal down just a little the miss goes away.

O2 sensor ??? Intake manifold leak?

O2 is less than a year old and I'll hit the Intake manifold with a torque wrench as soon as I can thanks for suggestion.

Also my harness was replaced 6 years ago.