Help me diagnose this problem: I can't rev past 3500 RPM intermittently (AK370Z)

Hitmeplease

i have the same problem with my 09 370z. This started two weeks ago when i was leaving work and getting on the highway, all of sudden it wouldnt let me rev pass 2500 rpm and the check engine light turned on. My car was towed to the dealership that night and they changed the valve timing control solenoid. I got my car back the next day, drove it for one day and the problem came right back the day after. Took the car to a shop and the mechanic scanned the car and got the P0021 code( camshaft variable timing control). He suggested that i bring my car back to stock(my car was uprev tuned) if the problem comes back then take it back. Any suggestion for me guys greatly appreciated.