The maximum speed you can possibly experience on your line is not the same as the maximum stable speed. You may simply have done your earlier speed test while the line was testing itself at the upper end of the range. As regards ping and upload, that's not something I have any expertise in. There are folks on here who are in to gaming and the like, so they tend to know more about ping and upload.
One thing you might try is running a test at
www.pingtest.net - it will give you some impartial idea of what your line quality is like. Run the test, then under the results click the button that says "Forum Link". Come back here and copy (CTRL+C) into a post so we can see the results of your test.
Here's mine:
