There was a guy at work that wanted to test a theory on his relatively new honda. Same idea, never changed the oil or filter. Simply added when it was low. Apparently he went 60K miles before the engine threw a rod. Just goes to show you that the recommendation to change every 3k miles is probably overkill.

Wow, just came accross this, Pontiac must have issued different owners manuals sine mine says 5quarts for the 400, with filter change for an AC car.

That's strange since all oil pans have the same size sump.
Have noticed some show little over/under full mark on oil changes.
Just figured was do to how far the lower tube was installed inside the block.
Wouldn't worry if little over since probly 2/3rds(?) are up in engine while running...