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.