A couple of things to check, first make really sure, I mean REALLY sure you have mapped your hair growth. I cannot tell you the number of times that guys thought they knew which way the hair grew and then were surprised to find it didn't.
What you think is WTG might not be.
Another is speed. Go really slow. If you think you are going too slow, then slow down.
Speed magnifies errors created by bad blade angle, which is another thing to check. Neck problems can often be attributed to the difficulty in getting the correct angle in that wierd location.
Don't over stretch the skin. You will find that just stretching enough to get a flat shaving surface without loose skin getting in the way is all that is required. Overstretching can contribute to ingrowns by cutting the hair below the surface. Some guys can get a way with it, most can't.
Good luck and keep us posted on your progress.
All that is necessary for the triumph of evil is that good men do nothing.