Tough one. This may require an adjustment on the TV cable. However if the TV cable is maladjusted, that could cause damage to the transmission.
You can find the [http://www.tciauto.com/Products/Instructions/instructions/gm_tv_cable_adjust.htm|directions to adjusting the cable here].
Good luck, I wound up having to replace my tranny. If you get a used one do yourself a favor and rebuild it before you put it in and adjust the TV cable before you drive it anywhere.
Regards,
Frank