Hi oskiatl.

If you are using the the latest Captain Sim 767, version 1.5, then what I have described above will not make any difference to the problems you are having with it. The 767 v1.5 does not need FSUIPC to be installed like it was for v1.0 through v1.4.

Give this a try:

1) Make sure FSX is shut down.
2) a) Vista/Win7 - Go to Documents\Flight Simulator X Files. b) WinXP - Go to My Documents\Flight Simulator X Files
3) Find the 3 *767-300 Captain Cleared for takeoff (KSEA) files. The file extensions are .FLT, .FSSAVE & .WX.
4) Double LEFT mouse click on the 767-300 Captain Cleared for takeoff (KSEA).FSSAVE so that it runs FSX and goes straight into the 767-300 Captain Cleared for takeoff (KSEA) flight without going through the FSX opening screen.

The idea of doing this is to see if it will work like it should by avoiding you default FSX flight. IF it works properly, you will at least have found a way to avoid the problem.

*767-300 Captain Cold-n-Dark (KSEA) could be worth trying as well. The only difference is that you have to get everything setup from the beginning. Just do a test flight from KSEA to somewhere and see if it performs fine, or not.

Out of curiosity, are you seeing the IAS/MACH Indicator displaying 000 and the Altitude Indicator displaying 00000? I have this happen this quite often when I load my CS767. If I do get it, then the 767 will not perform like it should (some buttons or switches don't work at all).
If you are, just reload the 767 using Alt > Aircraft > Select Aircraft > ENTER (to select the current aircraft).

Mark