3.4 V6 '02 PreRunner - Stumble during accel/hill

Can anyone lend some diagnostic help?
I purchased an '02 DoubleCab with 3.4L 9 months ago, it how has ~172k miles. Recently, the engine misses/stumbles when accelerating, or on a hill (in other words; under load). It seems to be getting worse the last 2000 mi or so. Some time ago, I had one of the O2 sensors changed due to a chk eng light.
Recently I ran a few tanks of Supreme fuel, have changed the air intake filter and the fuel filter. I am about to change the spark plugs (not sure of mileage on them); and if no help, my next step would be to change the spark plug wires?
I checked codes via NAPA and AutoZone, neither showed any codes; but a check engine light that had appeared very recently, disappeared after checking the codes.
Does anyone have any better ideas on where to go with this?
Thanks!

 

Id try the spark plugs and wires. Also maybe try a fuel injector cleaner such as seafoam or something similar. and fuel filter if it has one.

 

Thanks Wilcam47! ... I will try all this, the injector cleaner is a good idea. ... I changed the fuel filter, no change in performance.

 

I had something like this on my prerunner. Changed the spark plugs and the problem went away. Hopefully its just as simple for you.

 

Sounds like a timing issue. When was the timing belt changed?

 

The thought crossed my mind ... I had it changed almost 3000 miles ago; so it's not due to wear, but could it have been installed a cog off? ... wouldn't the symptom be more severe though? It starts easy and idles smooth.

 

I had this issue a while back and changed the spark plug wires and good to go.

 

I installed new spark plugs today (Toyota PN:

$8 90919-01192 Toyota Genuine Spark Plug

90919-01192 - std Denso dual electrode).
Problem solved!
I will probably install a new spark plug harness fairly soon; I ended up breaking the retention tabs off the connectors that plug into the side of the 3 coils. ... not sure how prone these connections are to coming off without these tabs ... but it runs great for now.
Thanks you all for your input; it was appreciated.

 

Appreciate you following up and posting the solution. This will be able to help others out in the future

 

Just posted about the same issue, lol. Getting new spark plugs Tuesday

 

Make sure you also get new plug wires, as they are often the cause, not so much the plugs, not that it wouldn't be a bad idea to change the plugs as well.

 

Got NGK wires coming as well. Thanks

 

OK, so more information on this one. ... Maybe unrelated to the original problem.
After the problem was solved originally above, after about 700 miles; a very similar symptom re-appeared; a miss under load.
The local AutoZone reader said the #5 cylinder was mis-firing. I changed the #5 spark plug only; but this made very little difference; although I detected what looks like a crack in the insulator.
I installed a new Toyota spark plug harness next with no improvement. I checked with AutoZone again, it was still saying a #5 mis-fire; and their per the code, their diagnostics said to change the #5 coil. It made sense, so I purchased a new Denso coil from AZone. All is good
now.
Truck on. ;-)

 

Clean out your MAF and throttle body while you are trying to find the problem. This can only help.
Good Luck,
Paul