Chevy Lumina Hard To Accelerate

I have a 1995 Chevy Lumina with 97K miles. I only had the car now for two months and everything has seemed find up until. When I start my car it will only accelerate to 20-25 mph and sometimes 30 mph then while driving it drops down to about 20 mph and takes about 5-10 minutes to get back up to 25 mph and stays there for about 2 minutes or so and drops back down. Sometimes when i'm driving it will stop and jerk and i'm able to drive up to 30 mph for a short while then the gage drops back to 20 mph. I smell oil or transmission fluid not sure which one it is. A friend told me to keep driving it until the gas get close to empty and put some fuel injection cleaner in it. Would this help? I know the car needs the coolant fix because I know it has a leak, the oil was recently changed too.