Gonna go check out a 07 GP GT with SC 3800.
137k on the clock. Of course pictures look like a million bucks. Had a Olds 88 with the L36 for years so I kinda know my way around the 3.8.
The GP is fully loaded but all those bells and whistles can cause some grief. What should i be watching out for on this rig?

How many miles on the current spark plugs?

Is it all ghettoed out like it'* been beaten and not maintained?

How dark is the engine oil before you start it?

Does the transaxle fluid smell burnt?

Start the engine cold (not warmed up) and listen for unbecoming noises.

Scrutinize the transaxle'* performance, especially when cold. No need to beat it, but look for overly-slippery shifts, flaring, etc.

Now how does it run warm (idle and driving)?