If you have the 46RE they are notorious bad transmission and has to be rebuilt with in under a 100K miles. Some don't make it past 50K. I had to replace everything you did to mine to fix it but it was taking way to long to shift.
I'm not sure which trans. it is,it has just a little over 100K miles on it.
So if it comes back that it's not anything elctronic what else could it be? I'm thinking maybe some dirt in the valve body screwing up a valve or maybe the the pump not making enough pressure to make it shift. It will shift fine once or twice then it will wind out longer to shift then not at all but if i shift it by hand it will shift!