ard and smassey321,

I thought I covered everything I've tried in the original post, but I failed to mention I tried doing what you suggested. Specifically, I unplugged the xfer case at the actuator and the issue remained. After unplugging it, I even removed the front driveshaft and took it for a drive which pretty much takes the transfer case out of the equation. I'm still highly suspicious of the trans pan. I had bought an aftermarket one. I'll probably buy a ZF one and see what happens. Losing suction makes the most sense as it would be a cause that would unlikely through a code.