You might check/replace your speed sensor in the tranny. Mine was doing that. But after I changed the sensor it still did it. Turned out to be the drive gear in the transfer case that turns the speed sensor was bad. Worn teeth and it would skip. The speed sensor send the constant speed to the PCM and it needs to know speed in order to shift properly. Mine was going in and out of over drive. After I changed the drive gear everything is smooth as silk. Hope this helps.