Knowing what pressings you have would probably help! It's the numbers/code that's probably on the spine.
Try finding your pressings and reading reviews of it on Discogs. It's quite possible that there are documented issues with your pressings (bummer if this is the case)
On the 33 1/3 / 33 RPM difference, there is none. 33 is just shorthand for 33 1/3.
Otherwise, assess your setup. What's between your table and your speakers? Do you have a dedicated EQ? If you feel comfortable doing so, take a look at the belts in your table, if they're off even a little bit, it can make all the difference in playback for songs that you're used to hearing be played perfectly every time through digital.
Hope this helps!