96 Trooper - AT Fluid blowoff

Hello -

Got the AT fluid flushed and re-filled about 18 months ago, and now whenever
it's relatively hot (> +80 F) and we drive for over an hour or so, the fluid
blows off down the right side. There is a metal tube coming up from the
transmission (passenger side of the engine) where it then goes into a
flexible rubber tube and back into the fender and terminates there. The
fluid runs out of the wheel well and then blows down the side of the truck.

The garage I had it done at says it may have been slightly overfilled and
when it reaches a certain pressure it blows off.

Does this sound normal? Anyone else seen this?

I believe this is the TH400 transmission - does anyone know if the blowoff
tube is standard on these transmissions, and if so maybe I could take it to
a GM dealer for a closer look?


Thanks!