How long were you sewing when you started to notice the jumping stitches? From when you started to sew or towards the end of the piecing?
When my machine has been used for over 2 hours continuously, the motor will overheat and stitches will start going wonky. If I stop and let it cool down, things go back to normal. I've taken apart the machine, oiled and lubed it to death a couple of times, tried changing needles and threads and bobbins, etc. to no avail.
I have found that consistent speed (not too fast, and not too slow) does make a difference in the quality of the stitch when FMQ - I'm still a beginner at FMQ and get lots of eyelashes.
I'm using the 14 needle regularly on my FW with excellent results. My tension is 0, set by the mechanic the last 3 times in the shop, even though my original manual says tension should be 3 for even stitching. I use Coats & Clark cotton coated poly thread.
On the older spools of threads (I have some going back 25+ years), I get a lot of shredding and lint these days (probably because the thread has dried out). I've never used the Hump Jumper, though it looks pretty handy for thick seams. I am using Singer needles only.
I don't usually have a problem with tension, etc. but lately have been playing around with it to try to get a better straight stitch. It's the feed dogs in my case being sticky about dropping down, and I haven't seen a solution other than the ideas in this thread.
Lots of good ideas here. I'm keeping an eye on it for all of the above reasons.