Will declawing help my cat stop being a d*ck?

I have a cat who is currently taking 2.5 ml of valium a day because he is such a jerk. He is very sweet and fluffy and purry, but will randomly hiss at, and try to murder you. He will be snuggling with another cat, then get up and scratch it. He is 6 years old, and my husband and I were worried he's in pain and that's the reason for his mood swings and aggression. Two vets later, we find out there is nothing physically wrong with him. Despite the valium, he's still a douche bag. I'm thinking of declawing him. I heard this can sometimes make cats nicer, but can also sometimes make them meaner. None of my other cats are declawed and I wouldn't think of such a procedure if he wasn't so violent. This cat scratched me up so badly when I tried to clip his nails that my doctor thought I was cutting myself. Any suggestions, advice, things of that nature?