Hey Brooks.
Regarding the Sarge: he's too powerful. It's mainly the items that do it.
Compare his stats to some of the game's most powerful monsters: against the Dhole , he could maximise his Will track (to get 6 dice on the Horror check) and STILL expect to roll 4 or more successes on the Combat check. He'd have a better-than-even chance of killing the God of the Bloody Tongue on his first roll, and that's if his Fight track is at the lowest possible value. Cthonians , Star Spawn , Star Vampires and Flying Polyps are a pushover for this guy.
If he's meant to be OTT, that's fine - the Sarge is a badass after all. But there's a reason that the Chef (from Innsmouth) starts with rubbish weapons. This guy starts with a set of weapons waaaay better than anyone else's. The list prices on the weapons do seem to be about right, but if you add it all up, isn't this guy "over the limit" for the dollar values of his equipment?
Usually a character who was this good at fighting at the start of the game would have some serious handicap. A max sanity of 3 is the obvious one - like the Soldier and the Gangster. But in Sg.t Slaughter's case it's probably still not enough. You'd have to tone down the items, too.
A few random thoughts:
Mamaluke Sword: putting this special ability (the 'shotgun' ability) on a one-handed weapon is incredibly powerful, because it applies to all dice rolled, including those from weapons in your other hand. So the weapon itself probably needs to be a bit rubbish. If the sword was only +2 one-handed, instead of +5, that would be more interesting too, because you'd have to get hold of a really high-bonus weapon in the other hand in order to get the most out of it. Also, it would probably be a bit more realistic, since the close-combat weapons in AH tend to have lower bonuses, reflecting their limited usefulness (because many Mythos creatures are so dangerous that you can't afford to get near them anyway).
M9 Beretta: once you've got a bonus of more than about +3, saying you can 're-roll 1 die' is almost equivalent to just increasing the bonus by 1 (because although it doesn't increase the maximum number of possible successes, you're very unlikely to get that number of successes anyway; you're almost certain to have at least one failure to re-roll). Of course if you used the M9 re-roll in the first round of combat and still failed the combat, you wouldn't be able to use the M9 at all in the next round. That's an interesting concept for a weapon, but in this case the decision of which way to use the M9 is not usually going to be a difficult one, since the 'Exhaust' ability only adds +1. This is particularly true for Sergeant Slaughter since he's unlikely to ever fail a combat check. So it would be more interesting if the weapon's bonus was weaker (+3) and the special ability was stronger (exhaust to re-roll any two dice). That special ability would be particularly interesting when paired with the Mamaluke Sword, since you could even opt to re-roll a 5 in the hope of getting a 6.
Aviator Sunglasses: These don't necessarily need weakening, although they are a bit excessive for a combat character with a 2-5 Will track. You could add a special ability which says "Any phase: If you ever fail a Horror check, discard Aviator Sunglasses." In other words, they'd be good for as long as your luck holds.