Not sure what you mean by shredding the vinyl, but heres what I know.
1. I would have thought you need to adjust the offset when changing the blade from a 45 to 60. If the cuts on letters such as o's & e's etc are not closing, its your offset, noticed yours is set at 0, try small increments.
2. Check that you haven't damaged the very tip of the blade with a magnifying glass.
3. If the cut is choppy, try spraying the tiny bearing in the blade holder with dw40 or innox. If it's sticky you will get a choppy cut.
4.If the badly cut section is only on one side of the vinyl, it could be the cutting strip.
Setting the blade depth.... I remove the blade holder and insert the new blade, then I hold the blade holder vertical like a pen and draw circles on scrap vinyl. Using hardly any pressure, it needs to cut thru the vinyl and just mark the backing paper. Install the blade holder and cut a star, adjust downforce if needed until it only cuts thru the vinyl and just marks the backing paper again. Using a small star (1/2") will soon tell if its not right as it will lift the pointed tips of the star.
Oh and 60deg are great for small text.
Cheers Gary