Well, turns out that it was the pump after all...I ended up returning it to my original incorrect configuration - E port blocked, T port to tank, and still had no power in the system (this originally provided great power to the steering cylinder, but overheated the pump super fast)
Pulled the T hose, put the end in a bucket, and fired up the motor. Barely a dribble of fluid, even at 3,000RPM. Swapped the pump out with a backup, reconnected both the E and T hoses to the tee, and bingo! Properly working steering!
Thanks for putting up with me
All this said, SHOULD I be running some kind of restrictor or anything else, other than wide open into the tank, on that E port/hose for now? My future plan is to use it for a hydraulic cylinder on the driveline disconnect, but I want to get the truck drivable first.