HelloCustomer unfortunately, GM as many other manufacturers have done, have made the Throttle Positioning sensor part of the throttlebody. It is not serviceable seperately, you do have to purchase the entire throttlebody. I've seen this before on other vehicles and I feel it's unfair to force you to buy a throttlebody, but this unfortunately is your only option.
The throttebody is part number 12568796 and it lists for $144.96. That part is available at GMPARTSDIRECT for $85.92. Here is the link for them.
Your JA Expert,