BlackBerry Pearl- BlackBerry 8100 Series Smartphone -

[#1]

I have been having a tremendous amount of problems with my 8120 pear freezing.  T-Mobile tech support couldn't figure out the problem, and sent a replacement phone, and the new phone had the same problems.  I finally figured out it was the SD Card causing the problems.  The problems started when I updated my device software to the latest version.  I had a 4G card in it for a long time without a hitch, I bought an 8G card, and didn't have any problems either for several weeks until the software upgrade.  Now my phone freezes with the 4G or 8G card, I even bought a new 8G card thinking that was the problem.  Any way to downgrade to 4.3 software?  Any fixes?