2001 Silhouette Premier engine issues sputtering?

I have a 2001 Sihouette. I purchased this van used about 8 months ago. Shortly after purchasing this van, I noticed that when I put gas into the car, that the gauge was not correct. Only at initial start up. However, when I stepped on the gas peddle, the gas gauge increased, the more I acceled, the more gas I had! (wouldnt that be great). When I stop at a light/sign, it slowly comes back down. That is not my major issue, but I am wondering if that now has anything to do with my current issue. I just drove to the store, a half mile away, when at the stop light, the van started to shake. It almost felt like I was running out of gas. I put the car in park and pressed on the gas pedal and it sputtered. When the light turned green, I continued throught he intersection, but the car hesitated and sputtered. I made it home, however, on a small incline up a hill, the car seem to really get worse. The "service engine soon" light came on and flashed several times, before going off. I bought this car from a relative, who had regular maintenance, and never any issues. I am hoping this is something simple. I have 123,000 miles on it. Any ideas on how I can fix this before my summer road trip?

First thing I would do is to get the codes read, (Autozone will pull them for you for free if you don't have a code reader.) Once you have the codes, you can have Autozone tell you what they mean , or you can post them here. Once you know what the problem(s) is/are you can get them fixed.