So the bow is only 88lbs? That's light for a warbow as you know, so theres something fundamentally wrong - either with your technique or with the string itself.
First question - is the string that you have the same as the one in the pic?
Second question - if it is, did you change the string at all - adding or removing twists or retying the bowyers knot?
88lbs should be absolutely fine with Dacron, considering it's an ok string material right up to 100lbs, and we're only talking about getting the bow to brace height which is a fraction of the draw weight. I think Del recently posted on his blog that an elm bow of 100lbs required 55lbs to get to brace height so I can't imagine the problem is the string. Trouble is, without seeing you do it it's hard to analyse what could be wrong. Don't suppose you can get to Rugby/Dunchurch tomorrrow eh? I amongst others will be at the English warbow stall and somebody would be able to help you for sure then!
One aspect could simply be that you're not used to the weight, and lack confidence in pulling a heavy bow straight up towards your chin - took me a while to get a good feel for it!