

Brass synchro on 5th wears out quickly. Easy fix. All you gotta do is pull the tailhosuing off
5th gear usually never blows. The c-clip pops off that holds the 5th driven gear on and the gear slides back.
Usually you just need to remove the tailhousing, slide the gear back up and install a NEW c-clip.
It's actually pretty common on fresh rebuilds because the c-clip stretches when you remove it and never fully seats when you reinstall it. It should be replaced anytime it is removed
Fifth isn't an acceleration gear! If you speed shift into 5th you will kill it almost every time. I don't know if that's what you did, but I don't know how else you could have killed 5th.
I will throw in my .02 for Astro, though. I love mine. Do it.
ill be on number 4 probably soon, my 4cy trans is grinding in 3rd an 4rth, and gets really stiff when i rip on it. im suprized its helf together this long on spray an me railing gears. any idea what it could be MUSTANG5L5?? i love the ratio's of the 4cyl trans, if i can fix it an keep it goin that would be ideal. 1st and 2nd gear are fine, no grinding even when i shift really fast.