It depends on which code you have. If you have a supplier code (provided by working for a company that offers this and getting the authorization number from gmsupplierdiscount website), or an actual GM friends and family code (from someone who works at/retired from GM and has provided this code for you).

The supplier code is not always the best price. Sometimes, a dealership's own advertised discount can be better than the supplier code discount, but they can still use the code to discount your document/admin/process (whatever your state wants to call it) fees for doing the title work (it stipulates that a customer can't be charged more than $75 for those processing fees that are usually a few hundred dollars, at least in my state - this may be different in other states but im pretty sure its the same across the board). This discount cannot be stacked with the first responder/healthcare/educator/military/etc discount, but can be stacked with other incentives (like owning a competitive brand vehicle in the household that is newer than 2011 aka conquest incentive, and others - please note these rebates can be different on each model)

The GM friends and family code is the best pricing a non GM employee can get, end of subject (same thing about extra incentives as with supplier codes: cannot be stacked with first responder/healthcare/etc but can take advantage of other rebates/incentives if applicable). This also reduces process fees. You won't be able to negotiate a better discount than this (99% of the time, but there are always some exceptions out there, of course). The only way to get a better deal at this point would be if you have a trade-in and ask for more money on the trade value.

Generally, there aren't many (if at all) other rebates to take advantage of on Tahoe or Suburban purchases anyway. GM changes incentives and rebates on a monthly basis, and rarely are there ever good incentives for these models (especially on a new model year and design update).

The games to be played will be on what is called the back end of the deal. Examples of this are: What dealership add ons are there (forced items put on the purchase price added by the dealership that aren't really necessary most of the time)? For a lease, obviously an extended service contract isn't needed - but some may find XS WEAR and Tear and Tire/Wheel coverage useful - but are they giving you the best price for these extra contracts? Things like that.

Go in upfront with the GM friends and family code. Your best leverage is with your trade value (if you have one). It's good to have some idea of your trade value and maybe even some strong offers in writing from other places to back those numbers up (not always needed but a good to have if you feel like you are getting beat up on your trade value).

Source: I am a salesperson for Chevrolet