2001 sonata speed sensors

My 2001 sonata had a code 0720 about 3 years ago. My tranny was doing all the things that a faulty sensor would make it do.
A mobile mechanic replaced both input and output sensors....I think...not sure if both. It cost no more than about $150.
Just recently same problem and same fault code...0720.
A shop just charged me $350 to replace both sensors but there is still a problem shifting between gear 2 and 3.
No engine light...just a sharp shift. When I took it out of the shop it even slipped between 2 and 3 but after a few miles went normal. However it still in not normal shift from 2 to 3 The shop says it might be a program problem not a hardware one???
Any ideas what to do

 

A mobile mechanic is a parts changer.
Trying to fix an issue with the car by changing parts.
Hoping to fix it.

A P0720 diagnostic trouble code mentions that it could be input and/or output sensors,
Corroded wires or bad connectors, contaminated or low tranny fluid, or malfunctioning shift solenoids.

First thing to do is to inspect the associated wiring and connectors.
Check tranny fluid level.

If no luck then look for a mechanic who can actually find the real issue and fix it.