D.H.
The other two post are good......but as far as the mouthing off, yes he is 5.....and if you don't stop the mouthing off now, it won't stop............you can not let him feel that it is ok to yell or be rude to you at all...............or anyone else for that matter.....does he have to have the last word? I had a son like that........it's very frustrating and he still does it in his 30's!!!!
You can try the don't talk to Mommy that way, it's disrespectful talk, but my guess is a time out is going to needed.......at least for a bit...........
Good Luck and try also, when he shares, is nice and doesn't talk back, praising him and maybe giving him a sticker or something off and on to show that you appreciate his change.
Take care.