I just bought a new carbon bike that has a dura ace cassette 12-23 CS7800. I really enjoy the bike but I've been struggling on the hills.I was told that if I change the cassette to a 12-27 that I would see and feel a dramatice change when I do the hills. Any suggestions

You will notice going up to a 27. Give it a try. If that is still not enough, you will have to consider a compact crank or higher tooth than a 27 (if you do that, you will have to switch to a mtn bike derailler). Like I said, give the 27 a try.

Two lower gears on the hills is definitely a change worth making.

This may be obvious, but if the 12-27 doesn't work out immediately, give it a bit of time (2 months of decent riding at least) before switching to something else.

I'm not a fan of the 12-27 if you ride in groups. It always seems like there is no right gear because there is a big spread between each one. The 12-25 will help alot, but will give better transition through the gears. It may require you to gain alittle strength too. That's not necessarily a bad thing. Be patient. Your climbing will improve with practice.

I think you just need to ride more and get stronger and in time, the 12-23 would be good enough for you. But, if after say a couple of months and you still find it hard, well, you shouldnt but if you do, then swap it out.

thanks for the info.. How much of a difference besides the price if I switch to an Ultegra 10 speed 12-27 instead of the Dura Ace 12-27

There is no difference between DA and Ult in the cassette. ~35g and about $90. The Ult should last longer.

By 'no', I mean, no difference you and I would notice.

I switched from a 23 to a 27 and it made a huge difference on SoCal hills. I do agree that sometimes I have a difficult time finding the right gear because of the spread but it's more than worth it when I point up.