Mechanics are not super human that can figure out exactly what is wrong the first time every time. Some have more experience, and others are basically minimum wage flunkies. SOME of the items you listed, such as the timing belt, are general maintenance items. They may not have been the cause, but could have needed to be replaced. KIA's are not known for being "great" cars, actually they are not even known for being "good" cars. Just take a look at the resale value. So it is just as possible that you have more than one issue, especially at 87,000 miles.
Now, have any "codes" been reported. Generally if you are having a Service Engine Soon/Check Engine light come on there should be a code that can be read. If so you should take it to a place that can read these codes. This would include any other mechanic, as well as some auto parts store. And NO doing this will not void out any warranties. They will read the code and let you know what the code(s) are. Some will charge you for this, but others do this as a "free" service.
Does this tell you exactly what is wrong, NO. But it gives the mechanics an idea of at least where to start. Then if you have a good mechanic they may even tell you what the possibilities are. But at least if they give you the code you can do some research on your own, to be more informed when you take it into them(or another mechanic).