4G is LTE (they are one in the same) 4G=4th Generation LTE=Long Term Evolution Just different names for the same service. If you are having data issues it could be a multitude of things, first off who is your carrier? Also speed tests can be a little deceiving. What people do not realize is that high speed tests use remote servers that are not within the providers network, or control. So if there is a slowdown outside the network they cannot do anything about it. Even within the network speed cannot always be guaranteed simply because you are using a wireless device that is subject to external interference. Now with that being said there are some troubleshooting steps you can take.
-After the update have you deleted the cache partition?
-Is this happening in multiple areas?
-Have you had someone else try the same speed test next to you on the same carrier?
-Have you tried other speed tests that use different servers?
Just a few things to get you started.