Irritation on the neck when I go ATG on the third pass

Today I made only 2 passes: One WTG except the neck(where I have irritation) where I went XTG and the second pass ATG everywhere.
Better results with no irritation.

try a sharp blade in a mild razor with a pre shave

i'd try other blades, or a different (milder) razor for third pass (i.e. a tech) ...or just a lighter touch maybe

Make sure you properly prepare your beard before the shave to clean and hydrate it. I shower and use shampoo and conditioner on my beard as well as my head.

Be sure you use a high quality soap or cream, properly hydrated. I have a tough beard and sensitive skin, but I can get a near BBS shave with zero irritation if I use an excellent soap. If you get irritation, do not try to get away with an inexpensive soap, however, you do not necessarily need an expensive soap. When lathering, make sure you get a good balance of slickness and cushion.

I do a four pass shave: WTG, XTG, ATG and then a XTG/ATG clean-up pass. I often use a different razor and blade for every pass. I like using a straight razor or open comb razor for the first pass for maximum efficiency WTG. I usually do the clean up pass using a mild razor using an extremely sharp blade like BIC, Nacet, etc. The intermediate passes can be done with a straight razor, DE razor, or SE razor, depending upon my whims that day. I can use the same razor and blade for all four passes, but I get a better shave with less irritation if I use multiple razors.

When shaving your neck ATG, it can be difficult to maintain the proper shave angle. Go slow and be sure to use only minimal pressure.