it could be a bad download or a bad install......i would factory reset it....should fix your issue

 

Instead of focusing on rolling back the update, you should pay attention to fixing your current stability/connectivity problem. Look forward, not behind.
All the apps you mentioned require online access, do these crashing issues happen with WiFi or mobile data (cellular), or both?

Just to clarify, this update was a monthly security update or was it indeed due to switching from Sprint to T-Mobile?
And if it was the switchover, your carrier presumably sent you a new SIM card and instructions on what to. Did you also have to alter your APN settings? Typically that's integral to the SIM and a minor T-Mobile update patch but if that didn't work out you might need to manually edit/alter the APN settings to work with T-Mobile's cellular service. Are now using T-Mobile specifically or a MVNO that used to use Sprint before T-Mobile bought them out. These are T-Mobile's but if your with a MVNO go to there web site instead:
https://www.t-mobile.com/support/devices/not-sold-by-t-mobile/byod-t-mobile-data-and-apn-settings

 

check this out:
https://www.engadget.com/android-gmail-stop-running-webview-234125352.html

apparently it is a known issue with google

thanx goes to @tube517 for pointing this out in a few of the threads covering similar issues