You need to reflash your ROM using ODIN. Usually I would not recommand this if you have never done it before, but since you are already stuck in a bootloop, there's not really much further down-hill you can go.
However I'm not sure what the forum policies are here for discussing ROM flashing (even if it's official).
Short non-descriptive answer is that you need to first completely wipe both cache's, then download the official stock ROM for your phone and reflash.
Thank you for the reply.
That is what I was afraid of. I don't want to do that because I heard that it voids the warranty and if something goes wrong in the process, I end up with a completely useless phone.
Earlier this week, I ended up taking the phone into one of our local T-Mobile stores. The rep that handled my problem informed me that the warranty with cover for the boot loop and that a replacement phone will arrive in a week.
You probably need to disable the Lookout Security before installing any other. That may have been the culprit but I'm glad the warranty took care of it for you.