There isn't a factory DA/SA or DAO handgun that's that low. 10, 12, maybe even 9. But 5.5 on a DA pull? Negative.
The Walther P99AS (along with its clones) is a pistol that muddies the water a bit. It is a striker-fired DA/SA pistol with a 4.5 lb. single-action pull and an 8.5 lb. double-action pull (after de-cocking).
However, if the trigger is cocked, the first single-action pull is equal in length to a double-action pull, but just 4.5 lbs. Every subsequent single-action pull is very short and still 4.5 lbs.
It's a very elegant system that combines the safety of a DA/SA pistol with the excellent trigger feel of a good SAO pistol.