Here is an odd one. I have a song with 5 mono audio tracks and a drum synth. The tune starts playing at the correct tempo then wave files slowly start to slow down their tempo. The drum synth (AD2) plays at the correct tempo all the way through. By the middle of the song the waves are about a full beat behind and then are a full measure behind by the end. I have made no tempo adjustments to the wave files at all.  My usage meters are only at about 1/2 on my first core and 1/4 on the other 3. I'm running Win7 64 bit on a quad core with a 7200 drive. This machine worked great with X3. I'm using a Line6 UX2, but may swap this out to a Mackie blackbird to see of that is were the problem may be.  Any Ideas?

Acid.  You are taking too much acid.
 
Otherwise, have you looked at your tempo map?  Is there anything there that shouldn't be?
 
Or, solo one of your audio tracks that slows down and export it; when you play that with media player or whatever, does it slow down?  If so, perhaps you have somehow corrupted your wave files unknowingly?
 
Do you still have the version that played with X3 ok?  I.e, if you didn't overwrite that cwp.  Does that play OK?  If so, export the waves that play OK, and then import them back into Platinum. 
 
When your cpu runs out of gas, you get a dropout, not a slowdown.

Lol. Acid! The tempo map is as it should be. I should also have stated that if I start the project in the middle of the song, the waves play back at the correct tempo, but then start to drift downwards. I have my latency at 2048 and the line 6 buffer at the largest. I do think this is a buffer/processing, possible vst, related issue but I have very little effects on the tracks. (only breverb prochannel, and 2 instances of EZmix2 for the guitar, and AD2). I have not tried it on X3 yet as this was my first new creation with Platinum, but will do so later tonight.

Hello there...
Can it be that the tempo (BPM) in AD2 is set different than the BPM in your Cakewalk project? AD2 should be set as "following the project".
 
Roel

+1 I think the sync to host button is on the Beats tab IIRC... If using patterns from within AD2 (no MIDI data in SONAR), check for that button.

Was the audio recorded into that project at the current tempo and ran in sync at one time? And the AD2 drums play in sync with SONAR's audio metronome if you enable it on playback? Make sure you have Timing Masters for Playback and Recording both set to Line 6 drivers.

Thank you all for the thoughts. Yes the timing masters for playback and recording both set to asio Line 6 drivers. I am not using any AD2 patterns as I created them drum parts by hand with the piano roll. I didn't mess with any tempo stuff at all other than setting it at 140bpm at the very start. As I initially recorded, everything was playing in sync fine. Then I started to turn on a few effects, swapped out superior drummer for AD2, and the tempo issues crept in (the midi is playing perfectly). It seemed the worst after I added the nomad stereo widener. I immediately removed it but the tempo issues persists. If I jump around in the song it starts playing fine, but then drifts off after 15 or 20 measures. 

Sounds like plugin delay compensation is wacked. If you disable all effects does it play in time?