I have a 1998 Dodge Dakota automatic. When i accelerate the transmission does not shift gears past 20mph. The speedometer keeps moving on its own.  The check engine light and the ABS light are both on. When i read for codes i got P0443 and P0720. i first changed the vapor canister surge valve  solenoid and the output speed sensor. After  the code P0720 came off however the truck still did the same thing. I changed the speed sensor but also the wiring and connector again along with the ABS wheel speed sensor. Nothing then i changed  the PCM all together. When i did the code P0720 returned. Yet still no change. Any idea what and how to fix the problem. I was told it can't be the transmission because it does in fact shift but does not go past 20mph.