Jack started preschool (so it is all day rather than a half day) in Jan and he still acts up when he gets home. I now have a lunch and drink packed and ready for him to start eating after preschool. Usually when we get home I have to get dinner sorted so I've relaxed the TV rules and let him relax on the couch and watch some playhouse for a bit. If I give him some space and give him lots of warning for things like dinner, bath and bed he is a lot better. Really I think its normal for most people to get a bit grouchy after a busy day so I try and keep that in mind.
Another great thing they pick up from kindy/preschool is delightful language so just be aware of that. Jack went through a stage of calling me a f*cking old b*tch, luckily it didn't last too long.
Good luck, I have found preschool to be fantastic for Jack.