I noticed you said that this is an intermittent problem.
The only intermittent problem you may have is that what you are implying is that it sometimes allows you to go a lot higher than 4000 rpms in neutral.
The torque converter does not like to be revved high with no load, as stated before, this is to protect the torque converter from excessively high static pressures.
Now that I looked through the forum, I thought I remebered asnwering this question before, but my response was missing. You must have accidentally posted this thread twice, there are also other replies in the other thread.
1999 Dodge Ram 2500 Cummins Diesel
2002 Harley-Davidson Fatboy
Merlin Extralight w/ Campy Record