EDIT/NOTE: The following is just based on my personal experiences with my previous GT and the catharsis caused by the experience. The text is 100% speculative in its sections concerning Roland as a company. However, all the facts concerning my use of a V-Synth GT are 100% true. (Just trying to save my ass, that's all.

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Sigh.
Even though this comes a bit late, I'm very relieved to see someone else has had sync problems with their GTs as well. After all, it WASN'T in my head even though that was suspected, too. Not by me, though.
I think I was back in the day the first one to complain about V-Synth GT's VERY sluggy midi/usb sync. I tried to fight it a short while and even contacted several people involved with the product (at Roland), but to no avail. I was even challenged whether the feature was useful at all - I still don't quite believe the local representant took me for granted. His cure for the disease was to save multiple copies of a patch with different delay/tempo settings. My counter question: "What if I need to change patches or tempo whilst playing?" Answer: "Well, do you have to? Why would you do that?"
Well... that's why it's called "playing live".
That was already back in 2008, I think. I feel very, very disappointed to see the problem still exists, which probably tells more about the priorities of Roland and their development teams. Perhaps my loud assumption about the VsGT's underpowered processor and highschool-coded junior level bugridden OS was true after all (well, at least the bad coding seems to be true). If it was false, they'd already fix it easily, but the root of the problem lies much deeper, I'm afraid. Someone has probably lost his/her face during the product aftermath. I'm afraid that Roland has lost their belief.
I guess their common conclusion right now is "we don't need to do this kind of products". Dear Roland: if you only did it properly and your marketing team knew what to do, they'd sell like hell. The GT was a step into the right direction, but unfortunately the product owner/quality assurance/whatever didn't do his/her best. My opinion, not a fact, mind you. I've got no idea about Roland's hierarchy. I'm just a musician.
I sold my GT a long time ago, after I felt cheated and very disappointed, and stuck with my XT - which worked pretty well, by the way. No sync issues. I also have sold pretty much everything else by Roland, kept only XT, JD-990 and SH-101, I'd say there's two modern day classics and an ancient one. Well, three, since there's a D-50 inside the XT as well.
Back in the days Roland was accused of me-tooing, they'd see some manufacturer producing a nice machine, and they'd go "me too want that". I'm afraid metooing days are back, the only hope being Gaia, but even that is only a smaller scale 3rd generation JP8000. They'd metooed themselves. More bread and butter, easy concept, easy (cheap) to manufacture. But every patch sounds the same - it's not a bad thing, but it emphasizes the fact it's a two or three trick pony, not an endless resource of incredible elements. Subtractive synthesis can go only so far.
The concept of V-Synth is not for the weak. It's been very challenging to both Roland's marketing and the end user. I remember a local music shop dude demonstrating a number of keyboards for a friend of mine and the shop guy passed a GT: "That's too hard to use and it doesn't have a good piano sound anyway". My friend was looking for A SYNTH. Not a bloody workstation. What a clown.
My friend instead bought a second-hand XT later on and is still my friend.
Myself, I've never managed to create such patches with other machines I've created for my XT. The thing is, if you feed it quality stuff, you get a monster out. A nice, well-behaving monster with a lot of character not present in any other synth.
Roland, you hear us?