As title says: loss of power and sometimes hesitation/stumbling with full throttle applied. Also sometimes it'll bog a bit right when I start going in the morning. From my understanding both of these situations are during open-loop operation, but I'm not sure which inputs/sensors it uses or ignores during that stage. It runs great just cruising around town, but I do seem to have bad gas mileage ~200 miles on full tank (though I'm sure my tires throw off the measurement some, and my area is full of hills).

Sometimes it'll pop codes when it stumbles, but just indicates multiple misfires, nothing else specific. I've replaced 02 sensors, maf (with used one), wires, plugs within the past year. But I bought el-cheapo plugs, maybe they're not good. Also, I have an exhaust leak which I think is between headers and first o2 sensors. So would losing some exhaust through that gap hinder the o2 ability to read? Though I have heard that o2 sensors are not used under full throttle.

 

Maybe clean your used MAF with made for MAF cleaner. Clean throttle body butterfly valve with carb cleaner. It does drop out of closed loop at wide open throttle normally.

 

Get CRC brand MAF cleaner.
With the truck off - spray it liberally right into the throat.

You can plunk your codes into:
http://enginecodemaster.com as say P0104 or such if your scanner does not know the codes.

When my 1997 Discovery did this - we replaced the two front O2's and the VSS.

Ours used to stumble on open highway at 60 to 70MPH.

But the D2 is all Bosch.

With yours - look for vacuum leaks that come and go.
Make sure the intake manifold is on tight.
Check the brake line has the red retainer clip on it for the input to the intake plenum.

Or your fuel pump is not delivering enough pressure.

 

If you have the live scanner - watch the O2's.
The sensor 1's in the front have to oscillate.
if they don't there is your problem.

 

How many bolts are on intake manifold please?

 

If you clean the MAF, let the truck sit overnight first. The metal sensor heats up to something like 300 degrees. Also, don't turn the key in the ignition. That enables the circuit.