slipping turbo 350 tranny

[chevy art]

my buddy has a beautiful 69 chevelle with a strong 355 sbc and a freshly built turbo 350 tranny(no more than a 1,000 miles on both). parked it in November and all was fine, took it out yesterday and the tranny slips in third gear under acceleration, he read the tranny dipstick 3 times( in neutral) and it showed a big overfill(probably about 3-4 inches up stick). i told him to check it in park. which i think is the proper way, and it still showed and overfill. bu less than when checked in neutral. and ideas why this tranny could be slipping, and showing an overfill. thanks art in NY

[chevy art]

PS forgot to sayin my post, that it is not a manual shift valve body, but it shifts automatically(if that make a difference in the evaluation of the slippage) thanks again art

[SupStk]

First get the fluid to the correct level. Surprised that much overfull it isn't pushing fluid out the vent.
Next does the fluid smell burnt?
The most likely cause is the direct clutches aren't holding.

[chevy art]

thanks sup we will check the things you mentioned, and maybe drop the pan after we check out what you talked about art

[Baprace]

Chevy art, that is common for a auto transmission to overfill the case when setting for a while, the torque converter will back drain and overfill the case, you have to warm the engine up and then check the trans oil while running, always take the lowest read, it may be only low on one side of the stick. You should also shift the trans from forward to reverse while running and then recheck the oil level while in park.

[chevy art]

thanks baprace. ill do as you suggested. art in westchester co. NY