I agree 100% 767.  I didn't use it much before the Block F was introduced, but now I have been using this Captain Sims' 757-200 and now -300 constantly and I absolutely love it.  I also own the 767 your familiar with and it is a fine airline too, but something that I am really impressed with on Captain Sims is how user friendly the mouse controls are in the virtual cockpit.
I have not seen a virtual cockpit that is so easy to control as the way Captain Sim has made his.  The knobs and switches work almost as easy as if you were sitting in the cockpit using your fingers.  It makes it a real pleasure to fly.
I was having a little trouble figuring out how to set the heading on the MCP, but once I got it figured out (click with both left and right mouse buttons) it also is the most logical and easy way to work the "SEL" button.
On top of that there is so much function and visual clarity within the virtual cockpit I just look forward to "climbing in" every time.
I am very excited about being able to use this fine airliner and very grateful to Captain Sim for doing such a great job with it. 

Great screen shots 767.  I always enjoy looking at good screenshots and Captain Sims' flight deck looks fantastic.

My auto pilot works just fine so I would have to say that your problem is probably with the other add-ons and not with Captain Sim's 757 Block F.
I would suggest that you make sure you have the latest FSUIPC, uninstall your add-ons and Cpt Sim's 757 BF, re-install Cpt Sim's 757 BF,  start the sim with the default Cessna at KSEA, fly the Block F to see if you still have the problem, then re-install each add-on until you find the culprit.  (Also remember if you want to start with the 757 "Cold and Dark",while you have the Cessna loaded, turn off the master switches and ignition, but don't turn off the avionics. That may cause problems too)
I don't use FS Passengers, but I understand that conflicts with airliner sims are not unusual with it.
I've used Captain Sim's support before with success.  I know that software support can become a massive headache if there is not some system of formatting it in place.  I've seen it on forums of other simulation developers and could actually hear the pain and frustration in their voice from dealing with massive amounts of customers on the same issue when I talked to them on the phone (actually referring to the support of the one you claim to be "going back" to).  They have a very good 767 model and there is nothing wrong with that approach to supporting it, if that's the way that they want to handle their support, but there is also nothing wrong with going by Captain Sim's requirements in acquiring his support when it is needed. 
There is no way that support can pinpoint a problem it they don't know the exact environment that their product is in.  It may seem like a little more trouble, but I can see the need for it.