Hesitation at speed but low rpm

[TrevoJreal429]

I have been having a random hesitation problem for about a year now.
The truck is a 99 sohc with about 190,000 miles.
I realize I can't expect it the have the power it did new but this has only been happening since about 10 months ago.
When I am on the road doing anywhere from 45ish-60 mph
with the engine doing 1,500-2,500 rpms and I hit the accelerator almost nothing happens.
I have to completely lift of the pedal and hit it again so it will down shift so I can accelerate, i'm sure thats giving me worse mileage than I should be getting.
It is especially bad when I am using the cruise control on the highway and I want to accelerate to pass someone, I will hit the gas and nothing will happen and then all at once it will rev up to about 4,000 rpms.

I have done research and done everything I can think of to fix it

spark plugs- motorcraft, wires were done less than 40,000 miles ago too.
cleaned IAC, MAF, throttle body, new dpfe.
Seafoamed engine through pcv and replaced pcv valve and hoses.
Pumped out 4 quarts of transmission fluid and replaced with fresh,
have done that every year for the past 5 years and the fluid always looks clean.

The check engine light has never came on .
I had 2 mechanics that were doing unrelated things drive it and they both said they didn't think it was the transmission.

I have used ford synthetic blend 10w-30 for the past 6 years on it.
I seafoamed it recently and it only smoked for about 15 seconds,
I changed the plugs afterwards and I regularly seafoam the gas.

Any ideas? I'm about lost on this one.

 

[2Petes]

Your throttle position sensor,TPS, may be worn out but guessing is expensive. A better obd2 reader will show the value the ecu is seeing as you press the pedal, key on, engine off or on. You can backprobe the sensor also with a multimeter. Reads should increase steady as you rotate the throttle butterfly.

@190k miles it may be time for 2 o2 sensors (pre cat)

 

[colintrax]

Could be alot of issues, I had this happen and it was my new spark plug wire was touching the head and got burned which made it ground out to the head whenever it would touch. took a real long time to figure out my brand new plugs were the problem. I couldn't feel it at high rpms or low speeds because there wasn't enough of a load on the engine to make it skip. Don't fear testing new parts.
Also, it should'a smoked way more than 15 seconds. Especially with that many miles.

 

[UMD]

Long shot but check to be sure the throttle butterfly is opening all the way. I had a similar problem where anything above 45mph was very sluggish to increase speed. 70mph was about the top speed and that was after stomping the pedal to the floor repeatedly. Going uphill, good luck.

I ended up placing a block on the pedal and observing that the butterfly was only opening about 1/2. Took out the floor mat and repeated the test, butterfly opened all the way. Removed floor mat, I have no problems with getting up to speed, or maintaining and gaining speed up hills.

 

[TrevoJreal429]

The problem is intermittent also,
happens about half the time under the conditions I mentioned earlier.

I checked the TPS and the throttle body and they are both working correctly.
Plug wires are good and in great shape.

Does this sound like a fuel problem?
I know the check valve on my fuel pump does not work correctly and I have to occasionally cycle the key to prime the pump because all the gas flows back into the tank after the truck sits for a few days.
But as far as I know the pump itself works as it should.

I am not much of a mechanic , but have somewhat of an engineering background and tend to over analyze things.

Any suggestions are much appreciated as I have ran out of ideas.
Thanks.

 

[UMD]

I'm a noob here myself, but as I was looking into the possibilities of what could be wrong when I was having the same problem; I recall one of the first things to check was the fuel pressure. There are several threads on how to do it, and what the "good" pressure level should be. The other major item I found to be a possibility via the search function was clogged cats.