Latest update. I pulled the DTCs when I first bought the truck and stored that info in the back of my mind. I assumed these codes were probably something to do with the BD Torque Converter lockup that was installed and that may have been the case, but with the transmission acting up lately, I decided to come back to them and see if they could lead me anywhere.
After some quick forum reading, I found that the governor pressure solenoid and sensor are common failure points that can produce these codes and all kinds of crazy symptoms including the ones I'm having. I don't like throwing parts at stuff without doing at least some diagnostics but when its my own stuff and parts aren't that expensive, I don't care as much. So I purchased a new Borg Warner sensor and solenoid. They came in a kit, and it was only about $60. After work today I picked up a transmission filter and gasket and +4 ATF fluid.
I dropped the pan, and there was a bit more glitter than I hoped for (especially toward the middle of the pan, some of it was a bit coarse) but no big chunks.
Old solenoid and sensor-
New parts installed in the housing-
Back in the transmission with a new Wix filter-
And it took 5 quarts of ATF (and holy sh*t is +4 expensive) to fill it back up, but I drove it and got it up to temp and it is shifting great. No hard shifts and no refusing to go into third gear. Fingers crossed it stays that way.
Unfortunately it is
still leaking. It's coming from the bellhousing. Pan is dry, lines are dry.
I have yet to remove the inspection cover but I assume it is either the torque converter seal or the pump seal. It only leaks when it is running. Either way, it's not a fun fix. You all know what it entails. I'll probably pop the inspection cover off next and see what it looks like inside.