4.2 f150 2001

well im new to this so here i go
i just bought truck and problem encountered is i floor the pedal & it sort of stalls, doesnt take off just stops let go of pedal and hit pedal 1/2 way increases mileage but slow..so i changed sparks,wiring, same result no change took it to autozone OBD11 only message was something about both banks werent burning up fuel right so they told me clean throttle body did so also some small part that sits on top of throttle had a bit of carbon worked a little better but now im back to base 1...can anyone help me figure this out or give advise?? thanks sorry so darn long

these 4.2 are notorious for intake plenum warping or cracked or leaking intake gaskets that set a lean code p0171,p0174,p1351,p1371.I know theres a TSB put out by Ford and they also sell a kit for around $200 that comes with a new plenum and all the gaskets you need.