Yep, mine let go while simply rolling into 3rd gear and getting into boost. The problem with the T-5's seems to be a comination of things. What seems to happen is while under excess torque loads (that can be seen with both powershifting or simply producing to much torque), the mainshaft binds on the counter and will obliterate 3rd. This is partially due to the weak case design, partially with bearing clearances...and partially with gear design.
Ive heard good and bad about aftermarket gearsets from places such as Astro. While some have excellent results, I've also heard of others that have grenaded their new gearsets just the same.
I myself ended up picking up a 3550 for a resonable price and swapped it in and so far...I couldn't be happier.