Mickey2

Viking / Husqvarna machines are usually manage well with most jobs, but I think the 360 and some related models was equipped with stronger than average motor. The old Husquvarnas too, like 19 and 21E. I would suggest keep on cleaning and oiling the machine the next two weeks, daily and persistantly, and to do a bit oftest sewing. It will make a big difference once the dried up oil dissolves and gets flushed out. The 360 and related models are prone to holding on to sticky dried up oil, and the solution can be either very diliget oiling routine or disassembling parts for a major clean up. A thorough cleaning with improve everything from noise, adjustments, settings, general running of the machine to stitch quality, etc...

All lids and plates needs to come off, the top lifted up, clean out all dust and fluff, detect all oil points and tend to them peristantly the next week or two.

How high does the numbers go on the tension dial? Usually it's set to some kind of inbetween setting for sew-all weight thread; which means if your dial goes from 1 to 10 it should generally have a balanced stitch around 5. A lot of tension dials is numbered from 0 to 9, but it varies.

As you mention it's important to match thread and needle size; for heavier fabrics and top stitch thread I usually go for Schmetz 19. It's the largest I can find in 705 type needle and a large needle can be an advantage for heavier fabrics. (There is a brand that carries size 20 and 22, if your 360 can take it, a lot of new machines max out at 18). It's the larger eye you need for top stitch thread. It will affect tension and stitch quality. The factory probably has a suggested needle size for your uphosterly thread, for brands like Gütermann you can look it up on their site.

You might have to adjust the bobbin tension when using top stitch thread and extra strenght thread, ideally it should be set to a certain tension. There are tension gauges and specs for this if needed, but you can manage with out. I'm sure your machine should have perfect stitching, and it's all about getting tension right and matching thread and needle size. I have had similar issues with reverse stitching, but except for a couple of cases (fine jersey knit with stretch) I have been able to sort it out.