Well, kratom is the only opioid I have much experience with, so I'm not too sure about cross-tolerance issues. How much have you taken? In my experience, kratom's therapeutic index (the difference between an effective dose and over dose) narrows considerably once tolerance reaches a point where you need more than about 10g at a time (and around 20-30g per day.) Once I reached that level of usage, kratom would only prevent me from getting sick; no "high" and not much in the way of pain relief. However, even though kratom ceased to have any noticeable affect, even just 3g/day was enough to considerably improve withdrawal when I eventually decided to get clean for a while. So I'd say if you've taken more than 10g in one go and withdrawal hasn't improved, you either need to find another strain/vendor or your tolerance is simply too high to benefit from kratom (though I think that's unlikely - I wouldn't really expect you to get any sort of buzz off it, but it should at least ease withdrawal symptoms somewhat).
If you're having trouble physically taking enough kratom, I'd recommend the "toss-n-wash" method instead of mixing with juice or making tea. Just funnel like .5-2g in your mouth at a time (aim for the tip of your tongue - it's seriously nasty if you accidentally get the stuff in the back of your throat), take a swig of water, swish it around your mouth for a few secs and swallow. So long as you don't leave the kratom and water in your mouth for too long, all the bitter stuff in the leaves doesn't seem to have a chance to dissolve into the water, so I find it less bitter and nasty tasting than mixing into a drink.
