3 yr old son throws a fit at daycare

My son is 3 and he has been going to day for 2 1/2 years.  Everyday he has always cried when we drop him off at daycare.  When we pick him up, he is happy and nice and everything is fine.  I figure its just seperation problems and he will grow out of it.  He doen'st go full time, about 3 or 4 times a week.  
Just in the last two weeks , it has gotten alot worse.  He is 3 now and they switched him to another class.  He has never had issues like this when they switched him before.  He will start crying, taking off his shoes and getting undressed in the car on the way to daycare.  When we get there. screams at the top of his lungs, kicks and screams, tantrum stuff.  He does this when I drop him off in the class room too.  The teacher says he calms down about snack time and forgets that anything has happend.  He has a ton of friends at daycare and the teachers love his attitude.  He helps clean up, he listens to the teacher all day long and never has another issue all day.  
I thought maybe he would grow out of it.  I dont hang around the class room when I drop him off.  I hand him to the teacher, give him a kiss and say goodbye and I'll be back, or daddy will be back, in a little bit.  And then I leave.  
Any advice on what I should do? I try giving him something to look forward to when I pick him up.  I try telling him that his friends are waiting for him. I try getting him involved in the check in and check out process. Most teachers will try to console him.  Even his old teacher has tried to calm him down and nothing seems to work.  
I know its just a seperation issue with him but I'm worried that when he starts kindergarden, it won't stop.  I don't feel there are issues at the daycare with his teachers either.  

[jdtm]

I suspect you're right - it's separation anxiety.  However, if it is separation anxiety disorder, then you are also right - your child will not outgrow it nor will it go away.  I might suggest you google the phrase "anxiety and school" or "separation anxiety and school" or "anxiety disorder and children" or similar words/phrases to educate yourself on this issue.  If you truly feel that your son has more than just "normal" separation issues, then speak to your son's pediatrician.  If he/she is unable to help you, then ask for a referral to a medical specialist with experience in anxiety disorders.  By the way, anxiety disorders are very common and highly treatable. From what you have written it does seem as though your son might have a "mild" anxiety disorder; if so, intervention suggestions from a professional should be of help.  I wish you the best ....