Ford F-150 - 1997-2003 :: Engine Only Bucks / Stumbles Intermittently And Not At Idle Or At Harder Acceleration

2001-F150 5.4 Eng. bucking/stumble. I think my problem is slightly different than what I am reading about. Here is what I get (125k miles):

* Engine only bucks/stumbles intermittently and not at idle or at harder acceleration (this bucking is really harsh and makes the truck feel like a learner trying to drive a manual transmission and it is jumping down the street). The engine stumble is not a regular timing such as a cylinder going out and staying out for a period of time. It is quite a random pattern to the jumping

* Originally thought it was humidity related, but now I realize it happens in any climate

* No stumble in neutral at any rpm... only at a stop if I put it in a power brake load.

* When the stumble shows up, it seems like the throttle is around 10-25% (my best guess)

* Sometimes goes days without issue, but sometimes every ride and virtually every acceleration.

* Normally no stumbling at highway speeds, unless going up a hill.

* Every time it stumbles, it can be eliminated by either backing off on the accelerator some, or hitting the accelerator harder.

* No engine codes or CEL has ever come on

* Fuel mileage appears to be the same before and after the trouble started

Here is what I have done to try to correct it:

-> Fuel related (bad gas)... tried to run the tank as close to empty and fill it with fuel from different stations... when this didn't work, I have added HEET to it to dry up any water in tank.

-> Fuel delivery... replaced the fuel filter... seemed to work for one day, but then the gremlins came back.

-> Fuel delivery... ran multiple injector cleaners through tanks of gas.

-> Intake... replaced the filter.

-> Electrical... I don't believe this is related, but my battery died... parts store tested the system and stated the alternator was bad... replaced it, and took the old one to the parts store for bench testing and it was 100% OK... even thought the old showed OK, I left in the new one as a precaution. Only other item was a set of plug changes around 30k miles ago... I think I put in the super duper Bosch plugs with a lifetime warranty.

Current thinking and items I don't understand:

A) The bucking is so severe, it appears to be a random harsh loss of either fuel or ignition. A component that has failed electrically should give me a fault code with this level of severity. No trouble codes or indicators to electrically sense this disturbance...

B) For the fuel path, the most likely item is bad gas and I emptied my tank by running it as close to empty as possible and then used different gas and HEET to eliminate water. THIS MIGHT STILL BE THE CAUSE???

C) Another one for the fuel path is an intermittent fuel pump electrical connection or a weak pump from a pressure point. But if this is the cause, then why does it dissappear upon harder acceleration?

D) One last fuel thought is injectors... perhaps one or more have a range of delivery that they don't work properly... but this doesn't make much sense as at idle and harder accels are fine

E) From an ignition standpoint, perhaps I have failing COP's. I have not just gone out an replaced them due to my limited budget and the difficulty I read about changing them. Again, if one of these is failing in an either open or short condition, the computer should set a code for a misfire for the related cylinders. I get nothing. Hence my hesitation in making this change so far.

One thing i don't understand from the various posts is that the cops can fail under loading. what makes this happen as electrically, i don't think they can detect a load or not? it is hard for me to also understand why my truck would allow me to back off on the throttle or hit it harder and the issue disappears.