Random Misfire p0300 HELP

[knscharf]

2000 chevy Camaro 3.8 engine. Have had a random misfire code for months, but smog is coming up now no one can figure out how the hell to fix this thing.
I have changed, spark plugs, wires, coils. I bought a new ICM from auto zone and put in it there, and changed all 3 02 sensors. Even put the fuel cleaner in the gas.
Nothing happened, car has to be driven about 40miles before that CEL comes back on. Run the code reader, comes up with p0300.
Car was taken to a shop, they replaced the fuel filter, nothing. They wrote “misfire 65mph under load 180 degrees.”
They also put in a new cam sensor and road tested the car but the light came back on so they put the old cam senor back on.
Took the car to a different shop they did a fuel injector flush. Light came back on after being driven.
After that the guy scanned the code on the computer and found that it was cylinders #1 and #6 misfire. He then did a compression test on 1,3,6. #1=125psi, #3=140psi, #6=140psi.
I am at a loose with this car, the second shop told me that he really has no idea were to go from here, that there is nothing mechanically causing the misfire that he can see. he told me to take it to a chevy dealer to have them diagnose it.
If you have any input on what the hell could be going on I would really appreciate it.
Help me please…. Thank you.

[NavyVet]

Do a fuel pressure test with a direct reading gauge attached to the test port.
Get a gauge with a long enough hose so you can tape the gauge to the windshield and watch it while driving.
Also, pull the vacuum hose off of the fuel pressure regulator and see if it has fuel in it.
If it does, the regulator has failed.