It is has been determined that my Dimension Pro plays any sound about 1.5 semitones lower.  It doesn't matter what sound bank is used.  The problem is the 48kHz sampling rate that I use in Sonar.
 
I need to use 48KHz because of an Alesis Ai3 8-channel to ADAT interface.  The ADAT clock serves as the sync source for my Focusrite Saffire interface.
 
I've verified that Dimension Pro works flawlessly, and it is 100% in tune, if I bump Sonar down to 44.1kHz.  However, that also means the ADAT is no longer available.  So how do I fix this problem?  I am stumped.

I don't see how that can happen, unless you mean previously recorded track pitch changes if you switch sample rates. I think that DimPro should generate sound at the correct pitch regardless of your sample rate when recording. Sorry I can't help but it seems like I'm missing a piece of the puzzle.

I've had similar issues back in the day of Sonar 4 and 8.
 
One thing that may inflict is if allowing shared audio drivers, and windows also is having the same interface. A single sound event from windows may set interface to something else. Sonar running 48, and windows suddenly changed interface to 44.
 
Also check you audio interface where it is getting sync from and if master, auto sync etc, and also playback and recording sync in Sonar preferences.
 
If using other usb audio stuff, some have usb mikes or usb guitar interfaces that also create an extra interfaces in the system.
 
General procedure is also to disable onboard audio interface in bios setup, not to interfer.
 
I came through using some of above to get it sounding right again.

Uh oh, looks like case closed for this issue!  The problem is with GTune (Feb 2015 build and earlier builds).
 
I have written the developer, as this appears to be a big ol bug.
 
To make a long story short, I confirmed correct tuning of DimPro using an external tuner, but GTune was not reporting the correct project sampling rate.  This info is displayed in the INFO tab.  However, after stopping and restarting Sonar's audio engine, GTune reported correctly.  NOTE: You must click the MAIN tab and then INFO tab again to "reload" the info, or wait 10 seconds.
 
EDIT: This is embarrassing.  Sorry to waste everyone's time.

Glad you got it sorted.  Would be fair/helpful if you marked subject as SOLVED.

2:43AM
Uh oh, looks like case closed for this issue!  The problem is with GTune (Feb 2015 build and earlier builds).
 
I have written the developer, as this appears to be a big ol bug...This is embarrassing.  Sorry to waste everyone's time.

Don't worry about it, you might save someone using GTune a lot of time in the future
 
The only "wrong" thing to do would be to double down about how much SONAR sucks because it can't even play instruments in tune, then after you find the solution, never come back to the thread and let people know there was a solution.