Thank you for your answer. I did what you suggested, renamed the modlet so it is last in the mods folder, but still a lvl 5 "military stealth boots" only has 3 slots for mods. All the other military armor parts have the proper number of slots (5 for a lvl 5).
The "military stealth boots" is not a mod, it is a vanilla game item, here is the entry in the wiki:
Military Stealth Boots - Official 7 Days to Die Wiki (fandom.com)
Sorry I did not even know this was vanilla lol.
It will need an XML change in Jax's mod by the looks, the vanilla item seems to have a naughty effect_group.
This is the code which applies it to the armor:
<append xpath="/items/item[starts-with(@name, 'armor')]/effect_group[contains(@name, 'armor')]">
<passive_effect name="ModSlots" operation="base_set" value="1,2,3,4,5,6" tier="1,2,3,4,5,6"/>
</append>
The effect group for the other mil boots is <effect_group name="military armor"> but for the stealth ones its <effect_group name="military without penalties">.
I am not really good with XML but I am guessing this will work (add the extra 3 lines to Jax's items.xml):
<append xpath="/items/item[starts-with(@name, 'armor')]/effect_group[contains(@name, 'armor')]">
<passive_effect name="ModSlots" operation="base_set" value="1,2,3,4,5,6" tier="1,2,3,4,5,6"/>
</append>
<append xpath="/items/item[starts-with(@name, 'armor')]/effect_group[contains(@name, 'military')]">
<passive_effect name="ModSlots" operation="base_set" value="1,2,3,4,5,6" tier="1,2,3,4,5,6"/>
</append>
I am sure there is a better way for the above but should work!