Hesitation on 2001 Ford Escape 6cyl.........

About a month ago it seemed as if the engine was going to die when sitting at a stoplight. I could hold the brake down and the accelerator a little and it wouldn't die. In fact, I probably wouldn't have had to do that to keep it from dying - I just didn't want to take the chance of being stranded at a stoplight. Then about a week or so later my wife and I noticed that it would jerk once very briefly while driving at highway speed. Almost felt like we were hitting a bump - that was how much of a miss it was. It has been very cold here, so we put some HEET in hopingn that might cure the problem. It seemed to for a while, but a few days ago the engine "emission" light came on and my wife said it was hesitating between 2nd and 3rd gear (30-40 MPH). We took it to a good repair shop and he ran the codes on it and changed a plug and a coil. He said to drive it for a couple of weeks and see how it did. Well, the next day it was doing the same thing again. He is going to run the codes again today, but he scared me when he said it could be a major problem. Any ideas? In doing some research on the Internet, it sounds like it could be any number of things. Big or small. Sorry this is so long, but.......
Thanks,
Dave

fuel filter, all "frauds" require new fuel filters every 15,000

Very cheap part and easy to install

it would help a lot if you could tell us what the code was. I assume its a misfire code for one cylinder.

It could be an EGR issue, or a vacuum leak. Pretty hard to tell without doing some tests. Too often, mechanics assume that a misfire code has to be an ignition problem. Too often, its an unrelated side effect

I highly doubt its a mechanical problem. Its probably something fairly simple. Just have to do the necessary tests to narrow it down.