Duergar shaman will be a very tough cookie to crack. I had 1k hp/mana on a duergar cleric back in the day without setting foot in Winter, Factions or Desolation.
That being said I fought Toten's slith avatar warrior and it was a pure stalemate. The one dimensional cleric tactics couldn't overcome someone playing correctly. That being said, there was no way for me to be killed save screwing it up pretty badly. It came down to me and him in Rheydin with me being able to cast out 1000 mana on offensive spells and heals and him chasing me. Even with only 4 - 5 rounds in combat (dual vuln weapons) I still had enough time to cast and move.
That being said - I hate attrition players. Simply hate playing against dirt;flee;sleep (lame) - probably why I'm always investing in poison casting eq 
I'm unsure as to what you mean by 'attrition game' so here is my advice on both:
Every 30 seconds there is a tick - so the ideal situation is to count to 30 in your head and sleep at 27 (I think Celerity posted something like this a while back). Over time you'll learn to time it so its second nature - much like I can put a dirt kick in just before/on the tick. Time and experience will assist here - in both catching ticks and getting on your opponent close to the tick to stop them.
With a shaman good players aren't going to let you mal them easily. They will want a certain chunk of your life for letting you land mals. I used to run by the rule curse + one other mal = run. It completely stops a shaman but won't give you the win either. As UC told me (he was instructed by OM) - land non-curables first and build to the nastier (but curable) mals. Personally, once the battle starts to draw out I tend to run off and hide in a deep, dark hole to 'reset' the battle. Get my hp/mana back to 100% (the shaman will do the same) and start again. Longer battles favour the shaman - wearing you down piece by piece over a number of hours (RT) is all in a days work.
L-A