thm400 drops out of 3rd gear

Can anyone tell me why a thm400 would drop out of 3rd gear at about 50 kmh / 30 mph? I have replaced the vacuum modulator and replaced several of the seals internally. I have also replaced the fiber plates in the intermediate clutch pack. The other clutch packs seem ok. All the sealing rings have been replaced. The valve body seems to work fine. The vacuum pressure at idle is ~9 inches of water. I don't know the oil pressure becasue I don't have a gage for that.

Any help would be greatly appreciated.

Thanks,
Bilsner

What do you mean 'Drop out'? When you romp on it? Or just while cruising at 30mph?

Is it a recent rebuild?

Sounds like line pressure problem...

it drops down into 2nd gear while cruising at 30 mph. if i slow down to about 25 then it will go back into 3rd. if i tromp it, it will go into 3rd at about 35 to 40 mph. the repairs were done last week. checking the pump it didn't look all that bad, but i guess it could still be that some how.

thanks for the help.