Ford Forum - Enthusiast Forums for Ford Owners - Van lacks power, shows lean bank 1 code

The issue with my van has me and 2 other mechanics stumped.
Over the course of 2 days, my van went from running alright, to having absolutely no power going up hill (like, had to drive in 1st/low gear, and even that only produced 15 mph) and did not want to accelerate much on flat land. It idles fine (maybe a bit of a nearly un-noticable tremble, but smooth nonetheless) and slow pedal pressure revvs the motor, but a quick press has lag.
I got a code P0171 (bank 1 running lean) and have looked into vacuum leaks and manifold leaks, visually inspecting everything and using a rubber-hose stethoscope as well as the carb cleaner spray trick. Couldn't find anything. I changed the fuel filter, thinking low fuel pressure, didn't help. Code reader shows approx 40 psi at idle, 1500, and 2500 rpms during live test.
Long term fuel trim on bank 1 shows 25% at idle, 1500, and 2500 rpms.
LTFT on bank 2 is normal (about 10%)
I tested the resistance of all 8 injectors, they were all 12 ohms.
COP's all brand new Accel's.
I cleaned the MAF with MAF cleaner, even though it didn't look dirty.
I removed the O2 sensor from bank 1 to see if a clogged cat was causing too much back pressure, but the hesitation still persisted.
Any thoughts?
Any insight would be very appreciated.