I have had the P0456 code from my CEL for over a year now. I have replaced the gas cap with three different ones, making no difference. One of the gas caps was a OEM one the
other two were not. Now I am also getting the P0455 & P0441 codes. Besides the gas cap what should I be checking?

 

There's probably another leak in the system. First check the hoses under the hood that connect to the VSV (Vacuum Switching Valve). Mine cracked twice right where it connected to a metal hard pipe and caused a leak. Replaced it with a new one and all good. Check this link for the VSV and hose diagram:
2006 Scion TC VACUUM PIPING
P/N: 23829 is what failed in my case. Yours may be different.

 

Thanks for the reply, I will look into that this weekend

 

I checked the hoses this morning and hose 23829 does have a small crack where it connects. I will replace this and hope that takes care of everything. Do you think it will also take care of my P0101 code? I replaced the sensor, but still get the code along with these eVap ones.

 

It fixed my evap codes (after resetting them). I'm not sure that it would be related to a vacuum leak, as that hose I believe is on the charcoal canister side. Still, if you have one cracked hose, you very well may have others.

First, I'd check all the intake connections after the MAF, then check every hose you can access. Finally, you can spray carb cleaner in areas that you suspect may be leaking. If you hear a change in engine RPM, that's indicated a vacuum leak.