T.S.
Hi T. and welcome to Mamasource.
Well, my DH and I work FT, too. And we had our second son in August 2007. Towards the third trimester, my son Jacob (2 at the time, now 2.5) became a Mama's Boy. Daddy wasn't allowed to do anything! Since I knew Ryan was coming and that I would be breastfeeding him, I stopped making myself so available to his needs. I didn't ignore him in ANY way, but I slowly started having my husband do more with him. Now, with both boys, we trade off all night. Feeding, diapers, bath, playing, etc.
At 2.5, Jacob still wants "Mama" for certain things. I HAVE to be the one to read books and tuck him in. If he gets up in the middle of the night, "Mama". But, when it's playtime (rough-housing), that's Daddy's job. We have a basement full of the toys I don't want around our good furniture and Daddy has to be the one to take him down there to play.
As for the talking back to you and not Dad. Jacob already knows who is the strict one in the house (me). He will raise his hand to hit me, but if I give him the "look", he backs down. Dad isn't so strict and Jacob will push the limits with him and will hit. He still gets the same punishment (time out), but I think that Dad allows a little bit more when I'm not around.
A part of your 3.5 y/o's resistance to you may be the new baby. As Mom, I think you have been tending to the baby now. And if you are breastfeeding - or were - even more so. Up until last week or so, I still nursed my 6 month old when I was home. (He stopped nursing for some reason and only wants my milk from the bottle). Jacob would get SO angry when I was feeding Ryan. So, there was some jealousy. Maybe your son feels this way, too.
If I were you, I'd take your older son out for a nice lunch this weekend. Just you and him. Hit McD or somewhere fun - as a treat. Take him to the store and let him pick out some books that are for him and MOM to read at night. We're big on reading in our house and I SO enjoy the time at night reading with my son before bed. He does, too.
I'd also start taking on bath time or play time or whatever and have Dad take the baby in the other room. If your son cries for Dad - tell him that he has to take care of Baby.
Not sure if this will work - just some ideas.
Good luck!
T.