PO720 Truck will not move

[Aubtigrz2010]

Recently rebuilt tranny, has worked fine except for flashing OD light for a few weeks. It started not having any power in 1st or 2nd gear but when in 3rd and up was fine. I made it home and it is just sitting. While in park it wont even rev up past 1500rpm. Something in the computer is holding it back. It is doing the same thing in Park 1st and 2nd. It just pulled a code PO720 Output Speed Sensor Malfunction. When the truck was in 1st gear trying to make it home the odometer went blank and had slash marks all over it. Do you think this is a bad PCM or Speed Sensor doing this? Thanks ALot

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[Mark Kovalsky]

It's the output speed sensor. That's what the code means. Either the sensor is bad or the wiring harness is bad or not plugged in.