Transmission problems

I have a 2008 Ford Focus it started
hesitating when it shifted from 2nd to
3rd gear black drove this way for
months I decided to check the
transmission fluid and couldn't get a
good reading so decided just to add a
little over a half a quart Evette shortly
afterwards I drove about a hour drive
and when I came to a stop I started
noticing my transmission was it
shifting funny and started to slip so I
would drive for a little while and let the
vehicle cool down until I got home
after getting home and next day I
drained I only pumped out but was
over full and which I should have
drained it all and change the filter and
fluid which I think is what caused my
transmission to do what it's doing now
I put a transmission additive in it and
drove it it was still going into gear but
it was slipping and the wrench light
came on on my Dash I didn't make it
home I had to have the car towed now
the only gear the vehicle will go into is
a reverse and when I put it into drive or
try to shift it down into first it just revs
up like it's in neutral another saying
besides the vehicle hesitating when
they would shift from 2nd to 3rd
before I overfilled it sometimes every
once in awhile it would just all the
sudden when I was driving it would act
like it was thrown into neutral but it
would go right back into gear my
question is as where do I start is it
best to just replace the transmission
should I try to replace some of the
Illinois. Get the codes red and I know
there's also an intermediate band or
bands know where do I go from here I
need not professional I'm very
mechanically inclined but just need the
advice from a professional of what I
should do next I hooked up a micro
mechanic plugged it into my Mike old
plug and it came back there was no
codes not sure if it's just cuz it was a
cheap diagnostic tool and if I should
try to get the code to read from a no
better quality code reader or you know
if I just need us a place that
transmission's know where do I go
from here please and thank you very
much