That used to be the 5 speed in my race car. I busted 3rd gear every 18 track hours or so. We could swap a trans at the racetrack in 40 minutes.
How long did it take to rebuild the transmission and did you just replace 3rd gear?
Usually just a 3rd gear could be repaired in about 2 to 3 hours. If things really shredded, the cleanup might take a bit more time. Teardown was a bit less than an hour… order parts… clean up the inside in the meantime, and a bit more than an hour to reassemble it. Tremec T5s are simpler than they appear.
Edit… To replace 3rd requires the entire countershaft be replaced since it is one piece. Then 3rd gear from the mainshaft.
“We don’t need no stinki’n 3rd gear” … lol …
I wished that were true! But road racing used mostly 3rd and 4th gears. With the T5, Everybody racing them knows not to gear them to use 4th - 5th gears as 5th is weaker than 3rd.
The problem was solved when I switched to a B-W T10 4 speed. It was known for this phrase…
If your right arm doesn’t hurt, you aren’t shifting it hard enough!
I hate getting good at a particular repair. I was R&Ring a trans so many times I joked to friends I should use wing nuts to install it. A friend that was helping me rebuild them finally said- it’s only metal dude! 
A semi-automatic with high line pressure, manual valve body, a ratcheting shifter and a lead foot are a sure way to repeatedly join the broken hub club.
Switching to a forged and machined hub eliminated that failure mode. I never did solve the foot problem 