3-4 gone again am i missing something?

[fullforce]

So my 3rd and 4th gear went out a year ago at 99,000 miles I completely rebuilt the trans (my first automatic) and it has shifted FLAWLESS all year and Ive put about 6,000 HARD miles on it since then.
Then today I left work at light throttle and 2nd was fine, 3rd was fine, then 4th was ok untill the converter locked then it went to NOTHING... had to go back down to 2nd and limp it home.

Is there anything that is a common problem to continue causing the 3-4 piston to blow? I know its a issue with these 4l60's but I thought id atleast geat 50k miles out of it.
Any advice for when I tear it back apart would be appreciated.