Just bought 99 GT. Check Engine Light came on

Just got a 99 GT today with only 64k miles. Upon taking it home I started to notice while in 5th gear any acceleration to get up to speed say 55 to 65 the car seems to bog or miss until i get a lil higher in the RPM or let off the accelerator. Lower gears seem to do the same thing if under 2k RPM. It was hard to keep up with the flow of traffic at 55mph because 5th defaintely did not like were it was at. Nothing Major. The Check Engine light came on about half way home and is still on. Got an appointment with my Mechanic on monday to give the car a better overview. I just bought it today so if not satisfied or finding a major problem I will tell the dealer i want out of the deal . Any ideas on what the problem might be? Car starts fine and overall drives fine with good acceleration in the power band. Plugs and Wires? O2 or EGR or other sensor? Or does it sound like something more major like a leak? Thx for Reply First time poster here. Second Mustang I have owned.

Sucks that you cant pull ur own code on these cars without a OBD. Ill be going to Auto Zone to see what the code is tommorow. Hope i didnt buy a lemon. Dealer said he drove 50 miles upon buying it and had no problems or code.....

Unfortunately i did not have the time to take it back. I called my dealer immediately and told him that the deal may be off and id be brining the car back and wanting my 3k deposit if this is a major issue. He got defensive and told me to calm down it could be anything. A Non blinking CEL doesnt always mean a major problem which i understand. Said to figure out what the problem is and get back to him first. I have some cheapo 12 month warranty from some place he gets it from. Where he said mechanics legally dont even have to honor it. He is a small time dealer with no service bay or anyone besides himself. Considering I just bought the car today and will not have a title for a week. Legally I can return the car monday and get out of the loan and my deposit money back Yes or No?