Surging, sputtering, loss of power at idle and low RPMs when HOT

[dlphnfn]

I was on a trip this summer that is about 2 hours from home. On the way back, I got about half hour from home and it started losing power and surging badly. I pulled off the road and it was idling VERY rough and surging. I milked it to a gas station, filled up and let it sit for a while. Then it ran fine all the way home (30 40 minutes).
When I got home, I cleaned the IAC and air filter and put a couple cans of injector cleaner in it (separately). I've been driving it to work, which is a little over 20 mintues, and it's been fine ever since.
Now, today, I'm on the way to the inlaws house which is about 2 hours, and it does the SAME thing at about the hour and a half mark!!! Surging, sputtering, and idle bouncing. I finally figured out that if you keep the RPMs up, it's fine. So I went 55mph with overdrive OFF and it ran perfect until we hit town where it was surging and sputtering again at super low speeds/RPMs.
I don't have my scanner with me (or my tools). Do you guys have any ideas for me?
Thanks!!!!
Erick --

 

[dlphnfn]

After it sat for about a half hour, I took it up town to fill up the tank. It started perfectly fine, idled fine, and ran perfectly fine. Filled it up, drove around at slow speeds for a while and it's fine. I'm not sure why this is so hard to diagnose... I guess I'll find out tomorrow when I go home!

 

[swshawaii]

I'd check for trouble codes first, CEL or not. Find an auto parts store with a scanner and get the DTC's. Cats OK, no foul odor?

 

[pcam13]

How much fuel pressure do you have? I've seen pumps start to go out like this.

 

[dlphnfn]

It's hard to find motivation to work on it because it's either me driving it for 20 minutes to work or my wife drives it 10... I pulled the codes, and nothing.
I was telling my wife on the way home that I thought it might be fuel pump related. Each time it's "acted up" I've stopped to fill up and the gas tank was under 1/4 tank and it drove fine after that. I've heard about keeping your tank at least a 1/4 full just for the pump to get cooled by the gas it sits in. Not sure if there's any truth, but it makes sense in this case.
Thanks for the ideas so far...

 

[Jbpul25]

I Have the exact same problem with my 2001 4.0 ranger, its runs great most the time. recently I had changed the pcv valve along with line and elbows, apparently the elbows are something that can crack easily with age. That made a huge difference for its idle but im still having the problem sometimes