'99 Alero 3.4L - problems, problems, problems!!

This may be shocking but I'm having problems with my wife's 1999 Alero....
It has a rough idle and I can feel a slight miss when running at about 40 - 45 mph.
It has lost some of the power it once had, especially going up hills and I really have to punch it when going up steep grades.
It feels like I'm driving into a heavy wind coming at me... or like I'm towing a heavy load..
I've changed plugs, wires, fuel filters, etc. but still have it.
Took it to Auto Zone.. the code reader said it was a misfire on cyl. 6.
I have roughly 100K+ miles on the car.
So far, my main troubles have been replacing hub assemblies (getting ready to replace my 3rd in 5 years)....
I really need to get this straightened out.... don't want my family to end up stranded, especially with colder weather coming up.
Any advice would be greatly appreciated.
Thanks..

There are three possibilities here. First, check the fuel pressure, this sounds like a fuel starvation problem. You have replace the fuel filter but with 100K on the clock it is possible that the fuel pump is failing. Second, you may have an injector issue. Injectors do go bad from time to time and since you have a misfire on #6 this would be a good indicator of injector issues. Finally, the transmission may be developing a problem. I doubt it but anything is possible. Check the fuel pressure first especially under load. If you see a major drop in pressure then the fuel pump is probably the problem. If that is not the case the injectors would be next followed by the transmission.

Thanks for the reply...
I had a feeling it might be an injector but wasn't sure.
There is another thing I forgot to add in the original post..
Within the past couple of weeks... we have been having problems with the cruise control not engaging....
One day it was working fine... later that same day... nothing.
Could the two problems be related?

On a lot of odb-ii DTC error codes that cause a SES light including misfire codes the PCM may inhibit the cruise control so the problems are probably related. We had a airbag fault light in our Alero with codes stored in the BCM module one time and it caused the cruise control to stop working.

I would also make sure you're not using Bosch sparkplugs/wires. GM engines don't get along with Bosch for some reason.

- Jeremy

I've noticed with my 99 every now and again the cruise control won't engage. If I switch the ignition off, then start the car back up it works fine. Only happens once every month or two. I figured it was something goofy with the ignition switch, since the switch has been getting harder to "unlock" as it gets older.