Thank you for your interest in helping.
Question #1: Yes, everytime I get back to 0.31.7 it gets fine, when I forward it to 0.31.8 it gets sluggish again;
Question #2: It happen the same, no change; Everything is really slow except downloading (as before);
Question #3: This is when it got strange! I never had connection threads panel active before, so I didn't had to turn it off. Instead, I turned it on. It got faster, more responsive. I then turned it off again, and then it got as responsive as with 0.31.7 again! So this was the trick. Just don't ask me why, since after that I got back again to 0.31.7 and then 0.31.8 and I had no problems whatsoever.
In short, there must be a bug somewhere, but at least for now it's solved for me.
Really thanks for your suggestions, and I hope I could help you make an ever better program.