No 3rd gear upshift

1-2 is fine. Rev to 4k, let off throttle and she shifts fine into OD. If I give it gas, at say 50mph, it will downshift fine into 3rd but will go back to OD as soon as I go to part throttle. Dropped pan, checked accum pistons.look fine. O-rings are ok, center shafts are tight, no slop. So, I yanked trans and stuck in another unit. My car is 99 gt and has 9BCB trans tag. Got a trans from 99 venture which also has 9BCB tag. Car shifts Fine with new trans. But I am curious to open up old trans and see what's up.

you lost 3 rd gear, time for a rebuild or a used one swapped in.

i am also a member of the i lost 3 rd gear club. it sucks. used tranny was the fix.

Other threads say 3rd gear sprag. And burnt band.

when you just pop the shiftier to 3 rd when at highway speed its kinda in neutral, when you give it gas it needs enough to power second gear, and its a lot like you know.

i drove for a good month like that, then drove it 2 hours to get swapped out. you dont even think about passing on the highway either lol

There isn't a band for 3rd only. The forward band works all forward gears. Likely it's a broken sprag or cooked third clutches. If you pull it apart, I'd think you'll find a ton of slop in the 3rd/input housing on the clutch packs.

been told if 3rd is gone, than i should not have 4th. i can drive all day in 4th just fine. i did see a slight variation in tach on 100 mile drive to dads shop. seemed to waver 100 rpm or so occasionally. but, old trans is out and sitting in corner.