OK been studding for the last couple hours. I'm convinced the problem lays in the vss speed buffer module, book says it's located on the brake structure. You have an input and an output sensor that are controlled by a steel reluctor wheel in the trans. The sensors generate power, imput goes to the pcm and the output goes to the vss buffer module. The front sensor is the imput, rear is output. The pcm calculates the difference between the two and controls the trans. The vss module is the componet that sends the signal to the speedo. the vss module sends vehicle speed and trans output speed to the pcm. The speedo is NOT fed any signal from the pcm what so ever. Did he replace the output sensor? If so it has to be the wiring from the sensor/generator, or the vss module. The module can't cost that much, but has to be replaced with the exact part number. Almost all trans codes are considered soft, and will reset with the ignition key, off/on will clear them.
The vss module will have 7 wires going to it c7 grn/yel from sensor, c8 blk [engine ground] c9 pnk/blk ecm-crnk 10 amp, c11 dk blu, c12 ltblu from sensor, c13 brn to pcm, c15 blu/blk to speedo.
Charlie