Upfront; this problem is very random. It may go a couple weeks or happen multiple times in a day. Truck has 97K, the PCM and throttle body were replaced at 82k as were the spark plugs. No DTC's at this time.

Symptoms
I'll pull out onto a road at about mid throttle and it'll just flat spot at 2000rpm. Applying more throttle to about 80-90% it'll gain about 5-8mph while remaining at 2000rpm and then "catch" and run like a bat out of hell, like a 90% throttle opening should. I have an Edge tuner on level 2, but the same situation has happened on each level 0-3. Sometimes this can be rather disheartening especially trying to pull out in heavy traffic on a 65mph road and I don't mean merging on the expressway.

Other little things like low speed surging will happen. In a parking lot at very minimal throttle opening <10% it will surge idle to 1200 or so and back down.

With little time on the PCM and throttle body my mind starts to go to the throttle position switch. So, how can I test/replace this or am I barking up the wrong tree?

 

Do you have any engine mods besides the tuner?

 

I've replaced the muffler with a flowmaster but the motor itself is all stock right down to the Ford Motorcraft Oil and Air filters.

 

A thought - take it to a muffler shop and get them to test the cats with an infrared probe - they may be starting to clog.