Hi and welcome to the forum,
Your trackball issue could be related to firmware or a memory leak fault. Try a battery pull reset first(remove battery for 30 seconds then replace) as this would be the easier of the 2 solutions. If that doesn't work, read on...
TMO is one of the carriers that won't let a search of their latest firmware without being a customer. You can pick up the latest beta firmware upgrade from here:
8900 Curve OS 4.6.1.250 Found Online! | BerryReview.com . This is version 4.6.1.250. You will need to delete the vendor .xml file to be able to install it (go to c:\program file\common files\research In Motion\Apploader and delete the vendor.xml file.)
Let us know how it goes or if you have any further questions.
Kind Regards,
Greg Myers