The slanted stitches are possibly an optical illusion and the advice Cathy gave you is great.
Here's Jenny's take on it: http://blog.sew-classic.com/2008/10/...-about-it.aspx

I like the darning foot that came with the 431G, its part number is 161596 if you can find one. They're pricey though.

Some people like the Big Foot - the purple one with the huge clear toe. I have one, I haven't used it much, because the first time i did, it made my 301 skip stitches. :thumbdown: I didn't take the time to investigate further, I'm sure it was something simple, but when all I did was change back to the Singer foot and the skipping stopped.... well, let's just say it's not top priority at the moment.

The one P60417 from Alphasew. http://shop.sew-classic.com/Singer-S...KED-P60417.htm I detest this one. Even though it has a clear plastic toe with a grid, it seems like I can't see what I'm doing.

Glad it helped. Different weight threads in the top and bobbin can tweak the stitches a bit. You can get around this by changing the tension on the top or bottom, but it's usually easiest to just use the same type thread in both.