Is it a Switch pitch converter or regular??
Do you have the kickdown rigged??
Also inside the Vacuum Modulator there is a adjustment screw to adjust the shift point. Not sure if you have this model, but worth a try. All you gotta do is take off the vacuum line and stick a small flathead screwdriver in the hole and turn either way to adjust the shift points up or down, sorry but I forgot which way is which....
My friend had a similar problem!!!
Hope you find this helpfull