I have been driving around for a bit now and it's getting progressively worse. I just threw a code, transmission component slipping. P0894. It definitely makes the same sound in park and neutral. It barely went up a very mild incline driveway from a stop.

The only thing I can do at this point is put the other converter in there and see what it does. If that fixes it, I'll probably upgrade my converter

 

I talked to the guy at Yank, and he's certain it's not the converter, or at least the converter is not the root cause.

He said;

1. An RPM flair up between shifts is certainly the tranny, not the converter
2. The whirring noise I described, he said would go away in Park or Neutral.

Of course, this weekend I decided to gut the garage and paint it, so I'm at least a week away from doing anything on the truck.

Back to driving the work van for a bit. Next step is to drop the pain and see what kind of surprises I have there. I will keep everyone updated. Thanks for your help.

 

Did you ever figure out the problem you were having? I am having similar issues with my set up