Sounds like the blade is binding in wet wood as there's not enough set on the blade teeth.
Ian at Tuffsaws has blades with extra set for just this purpose so I suggest you look on his website, tuffsaws.co.uk, then write to him for advice - better than phoning as he's very busy, and he will reply.
A 6mm blade sounds too small to me, and, as previously mentioned, you should be using the higher speed for wood.
Duncan