Stab always has downward lift!
Nose heavy aircraft in trim , stab leading edge down, with trim ND ( !!) , gives lots of down force on tail!
Rear center of gravity, less angel angel of attack on stab, but always positive.and less down force on tail.
At a extreme out of trim rear CG the 737 becomes unstable, like most similar aircraft ( Cessna 172 to 777)
On another note!
I was just in the sim and did a nose down out of trim exercise: I was PM we were at ca 285 kts and we trimmed ca 2 unit ND and PF could hold it with elevator.
Then we hit the Cutoff Switch and I tried to trim nose up!!
Could only do half a turn at a time, until we reduced speed, passing ca 250kts it got better and at 230 we both could get a turn a second and the Control Loading promptly dropped!
This was a Level D , B737-800 and I was in shock!
Bad news, if this is as per the aircraft!
I now have severe doubt the Max will be certified with ANY MCAS!
I think the NGs track record will save it, just!
Regards
Cpt B