For anyone still following this thread, I've determined that my Giffin Grip is in good working order and that my trimming problem is almost certainly my doing. Can't fault any of the machinery. I've been giving some thought to crutches. I guess I've learned not to use that term except for its literal definition. The use that has been adopted for our society seems to be "to use a thing as a way to avoid." I would add "to use a thing as a way to compensate." When one has handicaps, crutches are wonderful and allow us to continue to do the things we love when we don't have the ability to do them the "right" way. Clay is such a wonderful medium for all the people who choose it.
I've been making pottery for many years and was never any good at tapping something into center. One instructor enlightened me that it depends on the position one's fingers take when tapping and I had more success after doing it his way, but tapping doesn't always work for the piece. When I first learned pottery back in the early '80s, I was taught to use my needle tool (or fingernail) and lugs and that worked well over the years until I got my GG. I adore it because it saves me so much time and aggravation. I'm more toward the end of my creative life now, I'm still a hobbiest vs professional, and whatever makes my throwing days easier for me, I'll happily use as crutches and keep on enjoying having my hands in the mud. I love sculpting and hand building, as well, so I shouldn't have to quit working yet!
Thanks, Pres, for reminding me about the rims. I think that may be my total problem, but I can't put it to the test until I start throwing some more this week. If a jar is not level at the rim, that leans the bottom when it's turned over and thus a simple solution to my issue. No matter where the lugs are placed or the posts of the GG, the thing would still be leaning a little, wouldn't it? At least enough to make a difference in the trimming, but perhaps not quite enough to be obvious when I'm looking down on it and depending on the tapping, scratching, or the GG to get it right. Being more alert and more open to all the angles should do it. I appreciate everyone's input and I appreciate the differences in methods.