904 wont hold first gear

I rebuilt my 904 for performance and fitted a Transgo TF-2 kit. The car has a mild 360 but still has the stock convertor and 7 1/4 with 2.74 rear end.

The trans performs and shifts like stock. Soft shift to second, firm to third.
I assume this is because of the stock convertor and rear end. I expect there will be a change when I fit my 8 3/4 with 3.79 gears and high stall convertor.

My only concern is that I modded the trans with shift command feature and the trans does not hold in first gear. If I stat from a standing start in first it will shift to second as if I had selected second. Also it will not shift down to first when driving.

The mod has been done correctly as per instructions. I only ground down the 1-2 governor valve to .125". Should I have gone more? Is there something I my have missed?

Any help would be great.