My vehicle will stop accelerating while driving

2006 Ford escape, 50,000 miles. 3.0 I was on
my way to work one day and out of no where
the car just stopped accelerating when
pressing the gas. I thankfully was already off
of the interstate and was able to pull over.
Once pulled over I put it in park and tried
again. It would not go in drive nor reverse. I
turned the car off and waited a couple minutes
and then turned it back on and it started
driving like nothing happened but only for a
short distance than it happened again. No
check engine light. I took the car to the
dealership and they charged me 100 dollars
just to tell me they will have to open the
transmission and that would be 700 more
dollars. That didn't even include fixing it. It has
been sitting for a couple months now. I
recently bought my own scanner and I found
out it was showing code P0720. I have
changed the output speed sensor and also the
input but it is still doing the same thing.