"My truck did the same thing. I'd be driving down the freeway doing around 70 and the tranny would shift to neutral then slam back in. It turned out to be the sensor on the side of the tranny. I can't remember what they called it, something like neutral safety switch or something like that. I do know it only cost like $45.00 "
I have a 91 E250 with the E4od and I was thinking the shudder I get at around 60k's was the torque converter slipping, I've tried replacing all the fluid and filter a couple of times but no success.
But, I did get the code for the neutral saftey switch a few times and now I'm wondering(hoping) that it may have something to do with the problem....so, how do I check it?? I have a good meter and lot's of time!
I think the post you found is for the manual position sensor. I think the neutral switch is actually on the steering column, however I've never had any trouble with it. Shift your truck into park or neutral and then try to start it, it shouldn't start. If it does, you've found it.
You found a code for the nuetral safety switch? I didn't think there was one.