Um, that's an awful lot of stuff going on with 32-bit and only 4 gigs.....

Yup, I'd say check that you're not running out of memory and forcing the OS to do some painfully-slow page swapping. The first thing I'd do would be bounce down Superior Drummer or at least drop its voice count down to the minimum, and see if that helps.

Well as you all may know, Splat will not start for me anymore. (Gloucester startup crash thread).
 
So I opened the file in good old dusty rusty X3e.
It plays, I can hop around the timeline, and loop without drop out.
 
 

Are you at a point where you could free up resources that this project is using (freeze/bounce)?  Even if you try that as just a test (by creating a test copy of the project and working on that so that you don't adversely change your real project).
 
I think this project may have  bit too much going on for the available ability of your system to process it all.  Freeing up resources may make it possible to have playback perform without the dropouts.
 
Successive releases of most software usually results in them providing more functionality/features, but that also usually means they require a bit more system resources - memory & CPU, and while that can usually be absorbed on a computer where there is enough memory to handle the increase, for computers already pushing the edge of their limits, there may only be so much you can do - other than to lessen the demand on the memory and CPU power that is there.
 
You might also consider a test of loading this project (your test copy of it) in Sonar's 'safe mode', and skipping the load of all of the effects.  Again, this would be just for a test, to see if that would lessen the project's 'load' on the system, hopefully resulting in proper playback.
 
Bob Bone
 

Bob,
 
I'll freeze sup drummer - the only synth there and see how that goes.
It's country so we have oh and eq here a comp there some delay. Nothing so heavy
 
I guess I could look up and see where the CPU meter is too huh. Yeah that would be good.

Can you please list the plugins loaded into this project? 
 
Bob Bone
 

Oh I'm sure it's one of em. Prolly the old uad-1 stuff.
 
I'm just so enamored with my song I don't care much about the drop outs right now.
I'll address it later. Thanks for your concern though.
 
The drop outs are happening in this file with x3 where it's going to stay.
The CacheHash crash episode has me a little leery of the new stuff for now.

I generally run with my ASIO Buffer Size set to 128 for recording, and then bump it to 1024 or 2048 when Mixing/Mastering.
 
Bob Bone
 

This issue is solved! yay! man, that was a pita!
 
I replaced my old sata data drive with a new(er) one copying the files over (This by default does a defrag too).
 
Now I can click all over the time line while the project is playing and it does not drop out any longer.
It's been so long I'll have to get used to being able to do this again!