[asshanson]

I had a similar issue with my car and I found out the battery tie down came off. Battery was tilting under hard acceleration, arced a spark to the frame, and completely cut ECU power and bucked every time in 1st gear.

First you need to determine the root cause. For me it was physical acceleration that wouldn't been seen on a dyno. Other things like spark blowout or fuel cut or fuel pressure decrease you can diagnose in a controlled setting like a dyno. Maybe a weak spark system could cause that. Have you replace the plugs, wires, coils, etc?