My jerkey 93 Eord Aerostar

When I drive this vehicle in overdrive which I only use on the highway, it sometimes starts to jerk. The speedometer doesn’t move, and the Trans fluid is clean and new as I just changed the screen, and cleaned out the pan. I didn’t fins any metal shavings in the pan to lead me to believe the trans is junk, and it only has 25000 mls on a rebuild. I have been told it’s the sensor on the end of the speedo cable that is going bad, but my check engine light doesn’t stay on long enough to get a code reading. The vehicle doesn’t jerk when I drive if in drive, but the check engine light still comes on, I thought I should get a 2nd opp-onion If the trans before I start buying sensors I don’t need. If it is the trans going out I think I will change it to a stick is that going to be very hard to do?