My character wears full plate and according to the Core book, a gauntlet can be used as a lethal attack.
My question is Do I still provoke an AoO without the ImpUnArm feat. If so then why is the dmg still the same just lethal and not nonlethal like a naked fist?
One would think that a metal fist would do more than 1d3.
Yes, you still provoke AoOs. As to why a bludgeoning punch is less effective than a piercing one, I have no idea. My guess would be the same argument that applies to the monk wearing gauntlets... is it armor or is it weapon?
The Adventurer's Armory has 'cestus' in it, which might be something to look into if you really want them to be bludgeoning. Otherwise, you just have to shell out the extra 10gp for spiked gauntlets. I don't make a melee character(other than monk) without them anymore, the 'cannot be disarmed' quality is entirely to valuble to pass up. *shrug*
Gauntlet: This metal glove lets you deal lethal damage rather than nonlethal damage with unarmed strikes. A strike with a gauntlet is otherwise considered an unarmed attack. The cost and weight given are for a s ingle g auntlet. Medium and heavy armors (except breastplate) come with gauntlets. Your opponent cannot use a disarm action to disarm you of gauntlets.
Gauntlet, Spiked: The cost and weight given are for a single gauntlet. An attack with a spiked gauntlet is considered an armed attack. Your opponent cannot use a disarm action to disarm you of spiked gauntlets.