Hello and welcome to Just answer.com, Super mechanic here. About your vehicle.
There has been a service bulletin for that type of concern. Here is what it states.
with 4T65-F Transmission (RPOs M15, MN3, MN7, M76)
This bulletin is being revised to include additional diagnostic information and clarify model usage. Please discard Corporate Bulletin Number 02-07-30-013D (Section 07 -- Transmission/Transaxle).
Some owners may comment on any one or more of the following conditions:
The most likely cause of the various conditions may be chips or debris:
Technician Diagnosis and Correction
If the above symptoms are present proceed with the following steps.