When you choose the "Activate" option in pwnage or sn0wbreeze when making your custom firmware, sometimes it causes errors which involve the certificates that YouTube and push use. To fix this, you'll have to re-create your custom firmware, except make sure the "activate" option is not checked, and instead activate it with an old AT&T SIM and then unlock it through ultrasn0w.
Try making the firmware yourself. Make sure you don't check the activate option. Then once you've activated your iPhone with your old AT&T SIM, try playing a couple YouTube videos and downloading some apps that require push (Facebook) and then use it like once.
Then insert your T-Mobile SIM and see if that works.