I don't want to be mean but you have to think first about you are saying.
Latent Effect: Increases critical dmg
I thought maybe the latent is activated by simply doing a critical.
So, if you don't do a critical the effect doesn't trigger? Seriously? If by simply doing a critical, the belt would trigger you wouldn't need a latent effect. The belt would just say: Increases critical dmg.
my crits jumped from 150 or below to 180
You need a more mathematical approach to your testing as well as a target that would allow you to have capped attack on easily. Also, basically you are saying that the belt would give a bonus of 20% to critical. There is no other equipment that gives that much in the game. I understand that it could be introduced but that alone is a huuuuuuge bonus on a piece of equipment which I am not writing off as impossible.
Evis jumped from 1,500 to 1900+
Also, evisceration is not a good weapon skill to test specially on a mob that you have no capped attack against. Evisceration dmg can be all over the place and if you played long enough you'd see a much higher number than 1500 eventually if you weren't using the belt. Also on evisceration, your dmg went up by approximately 27% which isn't congruent with the % increase on your regular hits. Finally, I say no capped attack on because it's very few people in this game that have the joy of bathing in high amounts of attack.