Endeavor384

I run the PMDG 747-400X and the Captain 757 for FSX on my computer. However, I noted the 757 began to rock about its horizontal axis very erratically. So on Justflight's support it says to run the latest update for it; I did. Then it says to download the latest FSUIPC4 4.53 for FSX. So I did that. Then my 757 ran like a charm. However, then my 747 quit working properly. I could take off and climb perfectly. But once at altitude with the LNAV engaged following the course, the plane will bank to the right, then bank to the left, then back to the right etc.... The plane seemed like it didn't know where the course was, and kept chasing it like a new IFR student does when flying an ILS or LOC approach. Then eventually after a little bit of time, the plane will enter a 60 degree left bank, hold it for a few seconds, then completely roll over ON AUTOPILOT. So the FSUIPC4 fixed the 757, but caused problems for the 747. Are there any ideas as to why this is? I used to be able to run the both of theses with no problems what so ever. Also I have the latest service packs for the 747. FSX has SP1 and SP2 installed. Thanks. I know it is the FSUIPC because I installed everything with the 747, ran it multiple flights and was fine. Then I installed the 757 and installed the service pack to it. I tried flying it and it wouldn't fly. I flew the 747 again testing to see if just the 757 was causing the problem; nothing. Then I installed the FSUPIC and the 757 ran fine over 5 different flights, and the 747 crashed on the first flight. I just don't know what other options there are other than not running one airplane or the other, and if thats the case what a waste of money. If anyone has any ideas of where to even start that would be great. Thanks. Mark Carter