1999 Dodge P/u trouble

I have a 1999 Dodge Ram 318 with 110k miles on it. Yesterday my check engine light came on. As I was driving to the auto zone I noticed a difference in
the 4 speed automatic trans. It seemed to have trouble shifting from 1st to 2nd. It stayed in 1st gear longer. The tech at Auto Zone read the Codes and came up with error code P0720. The definition was A low speed sensor speed above 15 mph. Explanation was Vehicle speed above 15 mph while transmission output shaft speed below 60 mph. Probable cause 1. Failed output shaft speed sensor 2. Electrical problem.
Where is the speed sensor? I sure hope it is on the outside of the trans. Any help on this? Thanks
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Yep, it's on the outside. Look for a two-wire sensor at the back end of the tranmission, driver's side, in the overdrive unit. You unplug the wiring, and screw it out of the housing. Make sure the O-ring comes out with it. You should get a new O-ring with the new sensor. Lightly lube the O-ring with ATF, and re-install the sensor. You'll probably get some fluid leakage when you remove the old sensor. Have a pan ready to catch it, be ready to quickly replace the sensor with the new one, and then dump the caught fluid back in through the dipstick (goes without saying... use a clean pan to catch the fluid).
I
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Thank You Mr Tom. I will change it out tomorrow, that is if the Dodge house has one, and post my findings!!!
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Be nice if you got the sensor from the guys that read the codes (for free!) for you.

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Yup, probably cheaper as well.
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Replaced the unit ($24.95 + tax) and trans works correctly now! Check engine light still on though. Will it reset by itself or do I need to have it reset via AutoZone + a tip?
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Disconnecting the battery for 10-15 minutes will clear it - and reset your radio presets, too :)
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Again Tom, thank you and everbody else for helping me save some $$$ so I can buy gas for the truck...
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