Automatic transmission problems!

My 2000 SE has the 16 valve Zetec engine with the 4 speed automatic transmission. Just last week the trans has started to really act up. When the car is at normal operating temp, the trans engages second gear almost immediately from a standing stop, and does so very harshly. Then, on the 2-3 shift it slips badly. It goes into overdrive OK. I wouldn't say that I drive the car hard, no neutral drops or anything. Could the trans be overheating or could it be something else? The check engine light is on, it came on when all of this started happening. BTW the car only has about 61,000 miles on it. Too soon for transmission work, IMO. I've had the fluid changed about a year or so ago, maybe those numnuts at the shop overfilled the trans with fluid? ANy suggestions would be appreciated. :banghead:

Had it checked out, from what they tell me it is the throttle position sensor, had the fluid and filter changed and they said that wasn't too bad, nothing out of the ordinary as far as burnt fluid or metal in the pan. Keeping fingers crossed!