Suggestion for your problem will depend greatly on which
trans you have.  There is a decal on the driver door frame
with the trans code if you do not already know which.  If
you have one of the electronically controlled transmissions,
there is a good chance the MLPS sensor is bad.  This is/was
a frequent problem with them.  It does not/usually will not
set a fault code.  If you have not in the past, your trans
is well overdue for a complete fluid and filter change
including draining the converter.  If you have to have the
work done, you are probably looking at $250-300 in my neck
of the woods including parts at a decent independant shop.
There is no guarantee this will correct the problem if there
are other problems with the trans.  A good shop will run a
diagnostic scan before throwing parts at it and credit the
diag charge toward the repair if you tell them to make the
repair.

Lugnut

Have you ever had the transmission fluid flushed out?

I have a MPV minivan that racked up more than a decade of service and 100k
miles when I finally flushed the transmission. I paid $60 with a coupon for
the service call at the garage where I go for my smog inspections. The flush
solved many shifting related problems. My guess is that you have never had
the transmission flushed, and this is your problem. The banging and clunking
around can also be the result of broken mounts, but the description of the
symptoms you gave do not point to the mounts. You can replace the mounts
yourself if that is the problem. The guy that flushes the trans can look at
the mounts for you.