Just read the thread, and a few ideas came to mind so.......
Right, to start, the pears.
Pears, like apples, are already acidic. Not quite so much, but if you test some pure juice you'll know what I'm on about.
Now as pears, like apples (or even kiwi fruit for.that matter), should be considered "white" fruit. Which means that you should not heat process in any way. Because any heat treatment will cause it too have a "cooked" flavour which removes a lot of the "fresh" taste (I understand it reduces the acid). Hence its often best to just freeze the fruit and thaw it, then press it to get the best quality juice.
Oh and of course, heat issue can also trigger pectin clearing/haze problems.
The seemingly stuck ferment could be lack of nutrient, high ability/low pH, yeast having reached its tolerance, too low a temperature, etc etc. One of the current thinkings, is that no acids should be added during the ferment, as it can swing a marginal level to the too low area that causes a stuck process. Plus, acid blend has a mix that doesn't always suit the ferment i.e. the best mix I've found for traditionals is from Ashton & Duncans book (out of print) "Making Mead", which is 2 parts malic to 1 part tartaric. I'd guess it would also suit Apple and pear based brew......
Just my tuppence worth of course.........