Coolant/Transmission Issue Related?

My car (2000 Olds Intrigue GLS) was overheating a few weeks ago and my
coolant was low. I got the coolant topped off but it happened again. The
mechanic pressure tested the system but could not find the source of the
leak. He told me to keep driving it and bring it back if it overheats again. So
far so good until...

In the last few days, my car has been "kicking" in the back end. I think it is
when I shift of course. It even whined once, but only once. It happens move
often at lower speeds but sometimes at higher speeds as well. It's not
consistent and doesn't kick all the time but often enough to freak me out! I
am taking it in to be checked but I do not want to be unprepared for what
could be wrong. I also want to be able to discuss the matter intelligently
with an automotive professional!

Also, SOMETHING is leaking out of my car. There is a stain in my driveway.
We thought it was a small oil leak. Then we thought it was the mystery
coolant leak. Then we thought it was transmission fluid. We have no idea
what it is but there is definitely something leaking from somewhere! No one
has been able to find the leak yet, though.

So, what could the issue be with my kicking problem and could it be related
to my overheating problem or my leaking problem? Any advice or
knowledge you can give will help me not get ripped off! Thank you!