Car occasionally takes a few seconds to go at stop lights and won't shift out of first gear.

My girlfriend's car has 135k miles on it and its CEL on. I've had a friend
come out with his dad's Engine Scanner to read the CEL's and it popped out
12 codes:
P0102, P0128, P0315, P0496, P0641, P0700, P0717, P0751, P0756,
P0973, P0974, P0976.
I've been seeing my girlfriend for a little under a year and her dad has mostly
been doing band-aid maintenance to the car. For whatever reason he was
upset that we had my friend use the engine scanner to check what the
issues were.
We tried checking the Transmission Fluid by looking into the transmission,
but it was basically impossible because of where the transmission is on the
car. The radiator is really gunky with oil and my friend said that the head
gasket may be cracked and need to be replaced. He said luckily it doesn't
seem like there's water getting into the oil or the engine.
The friend that I had come over was a mechanic for a few years and he said
based on what I told him it sounds like the Transmission Control Module
needs to be replaced along with replacing the transmission fluid and a few
more things(most importantly the TCM).
Any and all help or input would be very appreciated. I mostly need to know a
few things like, Do I need to take it to a Transmission expert, would it be
better at this point to look for another car(aka is it worth fixing), and how far
gone do you think the car is at this point because supposedly they've driven
the living hell out of the poor car without really taking care of it.

If you have questions about the car I will do my best to answer them to help
you help me.