Problem with an add-on Citation X

The huge bump you're getting is a bug in fsx-- when you transition between weather stations that have different data, (say, wind direction and speed for example), instead of doing a smooth transition it's like you flew through an invisible wall and get thrown around.

Are you using time compression? I've had autopilot oscillate on me, but rarely below 4x time compression. The solution there is just to decrease it back to normal. I believe what's happening is that your computer's getting overstressed, so the autopilot can't make calculations quickly enough to keep you at the proper altitude. The framerate issue would suggest the same thing.

I'd check a couple of things to make sure your computer is performing at its best. First, make sure your drivers are up to date. Then I'd go through the startup folder and pull out absolutely everything I didn't need.
-hit start, run, type "msconfig" (no quotes.)
-go through the startup list, and uncheck basically everything except for antivirus, drivers, and anything that you specifically want to run on startup. (For example, if you have an hp printer you can uncheck the hp printer monitor, but leave the hp drivers checked.)
-Defrag your computer with a decent defrag utility. There are freeware ones out there that do well, but I also highly recommend Ultimate Defrag. The windows stock defrag utility sucks.

If all that doesn't work, try using a program such as smartclose before you play fsx! I'd also consider turning off antivirus while playing FSX, as long as you're not doing any web browsing or anything while playing. You're not going to get a virus from fsx, even if you're playing online, and AV can have a pretty significant performance decrease.

Thanks for the help. I didn't have any time compression on. I never do. I could try the msconfig thing, I've done it before with minimal, albeit real, results.

Now I know why when the game used to work that I'd be flying along and then WHAM the plane shakes and then settles back down. That's an awful bug.

My specs are this:

3.5ghz AMD
2 gig ram
200gig HD (with very little free space left, and when this drive gets full it gets SLOOOOOW)

I ordered a custom machine that I need to build but for the time being I'd like to be able to play and get half decent framerates. I don't know what to set my settings at to get the most eye candy for the least hit in framerate. I see tons of threads on it but I need something simple and down to earth. I'm not a software whiz and its hard for me to understand all of the garble that is spoken of the fsx.cfg file, although I have edited it according to some directions with just about zero effect, good or bad.

If your hard drive's full, that can have a huuuuge performance impact. I'd uninstall everything you don't have a use for, and also run probably the most amazing program ever created: Crap Cleaner.

Then, like i said before, defrag! Your hard drive fragments much more quickly when it's full. This is where the performance hit comes from. Defragging will work better and go faster after you delete the unnecessary stuff.

If you flat out don't have stuff you can delete, look into getting an external hard drive for putting stuff like music and pictures on-- stuff that takes up a lot of space but doesn't need high performance.

I can't seem to get it to follow the GPS line anymore. Does anyone know the steps to make it follow the planned course?

I'll load it into the planes flight computer, turn on the autopilot and hit nav and then hit the nav on the dash and it won't follow the course. Please someone help me!