Dave,
I have had the same problem on my older Stealth. We solved it 2 years ago (or rather Greg Goodall did) by cutting off the existing bolt ropes and replacing them with the next size up. We then had to increase the size of the 'feed' part of each slot to get the new rope in and also had to run a piece of sandpaper wrapped around a drill bit along the slot to ease it in about 4-5 places. It took a while but I was VERY pleased with the result as the tramp is much tighter than it had ever been before and has never pulled out since!