Ok here's the rundown car is a 1998 transam with a lq4 408, yank 3600 multidisk torque convertor and has a f1a procharger on it.

Now the problem on the dyno with the convertor locked it slips in 3rd around 3600 or so. Tried it in 4th convertor locked was fine.

Here's the thing that's weird on the street locked in 3rd convertor locked it holds be brake stalled.

If the band's were fried would it still hold doing that?

I plan to have it rebuilt. Could it be something else?