2nd gear problem TH350

[Malibu355]

I am having an issue and was wondering if it was an easy fix or rebuild time. During normal driving the 1-2 shift is fine and firm. During very hard acceleration the 1-2 shift slips so bad you cant even tell it shifted into 2nd. The 2-3 shift is fine. This is being manually shifted. Any help would be great.

 

[81Elky]

Your making decent power, I'd say rebuild time

 

[Malibu355]

Took it to the shop for a build up. Also changing converter to higher stall. Check the classifieds to buy my old converter.