PLEASE HELP!!! 3.5 Acceleration problem

[VQ35Altima]

Hey NicoClub...
I have a 2k2 Nissan Alitma 3.5 and love it ECXEPT after it's warmed up... When I start my car and let coolant temp reach about normal "just under half" drive off, the car feels great as it should. After driving about 3-5 minutes, I loose a good amount of power, especially under 4k RPM but throughout the upper powerband as well. It sounds like it's misfiring and getting starved of fuel and throttle body IS opening all the way... I have also noticed that my SES light does not work... So I had codes pulled and came up with:
P0021 "over advanced timing"
P0300 "Multiple random cylinder misfire"
and evap gross leak "gas cap???"
Has anyone else experienced a similar issue??? I really need some help figuring this out. I don't want to sell my car since i just got it. This is driving me crazy. I replaced both primary O2 sensors and I did check my Intake Valve Timing Control Solenoid and It seems fine "clicks on and off". Please help! Thanks

[VQ35Altima]

Anyone??? Do I just have a freak motor?

[DJ_B_Easy]

BUMP to get the OP some help...

[QR25DE]

P0021 - Prob cam position sensor is bad.

P0300: I would replace the camshaft position sensor since you are receiving the code for it as well. But the following could be the cause if that does not resolve the issue.

Faulty spark plugs or wires
Faulty coil (pack)
Faulty oxygen sensor(s)
Faulty fuel injector(s)
Burned exhaust valve
Faulty catalytic converter(s)
Stuck/blocked EGR valve / passages
Faulty camshaft position sensor
Defective computer

"I replaced both primary O2 sensors and I did check my Intake Valve Timing Control Solenoid and It seems fine "clicks on and off"."

I doubt you had two bad o2 sensors.