Thanks Iain, AEAJR and BeanerSA for your replies.
Thanks about the advice about the barlow AEAJR I didn't even know that barlows came in 3X so something for me to consider down the track.
I probably will try a 5mm eyepiece Iain in the near future so thanks also. When I first viewed Jupiter thru the Tasco it was fantastic because I wasn't expecting to see much, so I guess I just expected alot more from the Dob. Even with the Barlow there doesn't seem to be much difference so far but I have only viewed Jupiter a couple of times so far and on both those occasions it had been very hot the day before.
Thanks for the compliments BeanerSA and about Dobson's hole.
. I'm going to have to name it "Dobson's Sink Hole" when observing too close to the horizon.