1998 Pontiac Bonneville check engine light and spuddering

My 98 Bonneville has been running fine lately, but when I started it up this morning, it sputtered as I started going up a mild hill within the first minute of driving. It just didnt have any power. At 3500 RPMs it was barely accelerating. I took it out of gear and it seemed to be idleing fine, but the problem persisted as I continued to drive to work. Im not sure exactly when it came on, but I noticed that the check engine light had come on as well. After about 10 minutes of driving, the problem seemed to improve tremendously. The car didn't struggle as I drove to work, but I did notice a few sputters as I sat at traffic lights and when I accelerated at a very slow rate. Unfortunately, the check engine light is still on. Any thoughts?