I have recently returned from the South Atlantic and completed the Hadrians Wall Walk, and a tour of the Cairn Gorms, using a 60 Ltr TISO pack. I am looking to go lightweight and have since replaced my tent and other items, but now looking for a good light weight cooker which will work above 3000 mtrs and also a Pack that is less than 60 Ltrs and more than a 30 Ltr pack (I currently own a Osprey Pack which I love).

Any help?

Tynesider, if you like Osprey packs then the Atmos 50 would be worth a look. Other packs in the 50 litre range I've found good are the GoLite Jam and the Lightwave Fastpack 50.

Any stove should work fine above 3,000 metres. It's temperature rather than altitude that can make a difference. And because of the reduced air pressure gas canister stoves work better at low temperatures at high altitude than low altitude! There are plenty of ultralight little canister stoves like the Primus Micron, Coleman F1 Lite, MSR Pocket Rocket and Optimus Crux Lite that are excellent. If you'll be using the stove at low altitude in sub zero temperatures then a heavier remote canister stove like the Primus Express Spider would be better.

I can vouch for the golite jam, I've got the older model which is without the new back system and waist pockets however done many multi day trips in it. You need to pack carefully though and the only change I've just made is to put an extra piece of foam in the back support just for a bit more comfort from the odd bad bit of packing.
I like the idea of not having things all around outside and the side stretch pockets are great for 1 litre bottles.
All the packing is done in individual dry bags to make organisation easy.