Weird experience

I'd check the front before the back.

Fuel Filters? How many miles have you done?

Fuel filters could well need a change at 25k. They normally show signs of being fooked by the engine cutting out under heavy breaking though. Not sure why they would make the bike sluggish when the engine is cold but be fine when warmed up? An odd one this. Brakes would seem odd as well for the same reasons. If you don't notice it wheeling the bike around before you set off why would it be doing doing it in the first few miles of riding but then disappear? Everything expands as they get hot so should get worse. I had a problem with a front calliper sticking a couple of years ago but it only stuck when the bike was being ridden hard. I would def check the brakes and make sure they are clean and working properly though.

do you run with o2 sensors? could be a fuelling issue when cold

yeah, i am thinking fuel filters as well.
change em, as its time anyway, then re access.

Hang on I've just realised the original posting was months ago. Is it still doing this since you put in the
new battery and regulator?

If not the post solved with the reason.

Ok, You haven't had your throttle grip off by any chance?