1998 Grand am se stutters at 50 mph?HELP

[ms keaghey]

I have a problem,I Purchased this car 2 days ago,Paying 3500.00 from private owner>I had to scrape up that much!Today all excited to take my mom on a test run in it,i was on a deserted highway running at 50 mph,as I pushed the accelerator to speed up a little quicker,the car began sputtering,when I released the gas pedal,it quit.I also noticed the RPM gauge didnt move up at same time I pressed the gas.If my car is driven very slow and very easy,it does not do it.But if I drive any faster than a grandma it acts nuts.I purchased a high quality fuel injector cleaner at local parts store,but its not working so far.I would like to add that the car is the 4 cyl. with DOHC but has NO power.It drives like a basic 4.My previous vehicle was also a 4 with DOHC and If I gave it gas,it accelerated really well.It was a standard and the grand am is a automatic,therefore that may be making that difference.Please offer any advice on what to look for and all suggestion are appreciated.

[skibum1111]

Welcome. First, with an automatic your car will be a little slower, but shouldn't be all that much. Sounds like you have some maintenance issues, or more likely, lack of maintenance. Start with a basic tune up, plugs, air filter, things like that. Also, the throttle position sensor might be bad, and the throttle body might be dirty as well. Throttle body cleaner can be gotten at most parts stores, follow the instructions carefully. Good luck, if you need more information let us know.