I rebuild a 1999 4L60E transmission last night and put it in to day since thrid gear went out due to a check ball stuck in the valve plate anyway, after a few try going through the gears with the rearend off the ground the tranny did fine went through all the gears with ease. Then, on the 6th try I put it in first it had a rattle like something was trying to engage so I stop put it in reverse same thing? sounds fine in reverse also if I leave it in drive and go through the gears its fine. Something isn't right like something is trying to engage. I put in the TCI kit if its any concern. I havent took it up the road yet alittle worried. One more thing, I drop the car and put it in 1st move a few feet no noise same a reverse? Im completely puzzed!!

 

Whats up everybody. I found this issue several hours after I posted this so, I’m just now getting back to respond. It was the reaction planetary and the sunshell. Replaced the whole planetary assembly and does great. I have already put way over 500 miles on it and it shifts so much better and firm with the TCI kit, servos, shift kit and planetary assembly.
Thanks for looking for anyway.