shifting problems/erratic speedo
 

Hey guys , I originally posted this in the GMC area with no responses, so I would like to try here. I have a 3500 7.4/4l80e. It is shifting between 3rd and ovr dr. It is also holding gears longer than what it usually does. The speedometer is not raising above 45-47 mph. The fluid was clear and I changed the filter. I changed both VSS's. There was no change. I only have one 02[po161] code up . I am waiting for the probe and that should clear that. I am thinking PCM? Am I missing something. ANY responses would be appreceated. Thanks in advance Cort