mid to high 80's temp. 1/2 hour of stop & go City traffic.  
Running A/C, gauge never exceeded the half way mark.
Stopped it, went inside one store, came back out started right up, drove it another 100yds. shut it off, went inside for <10 minutes, came out started it up and it ran very rough, wouldn't rev or rise above a low idle....shut if off, gave it a minute, re-started and it was even worse.
So I figure it's hot and "vapor locked"  let it sit a half hour, spun over but wouldn't fire up...tried it several more times over the next couple hours until I finally killed the battery.
Towed it home, recharged the battery overnight, started right up this morning just like nothing ever happened.
As a matter of precaution I'm going to change the fuel filter as I've no idea when or if its ever been changed.
I though at first the inertia switch might have flipped out, but it wasn't popped.
I didn't have any tools or a test light to check fuses or relays.
I did depress the Schrader valve on the fuel rail and it sprayed until de-pressurized, later I turned on the key then checked it: no fuel, so I figured it was the pump.....still it started up like nothing ever happened.
Any ideas?

did you check the alternator output? fuel filter?

Sounds like your on the right track. Check the  fuel pump relay. You may have a corroded connection there as well. It has been my experience as heat rises so does the resistance in a failing circut.

I didn't check the relay, but will.
Corrosion is common here, but this truck came from Arkansas with one partial Winter here.
Alternator doesn't present any problems.
Fuel filter is an unknown. I did take a heavy folding knife and rap on it in case it sucked up a bunch of trash; had I not been in the spot I was, I would have taken it off, tapped/blown through it to check for contamination. I will be replacing it tomorrow as well as checking every connection I can.  I'm glad the pump hadn't gone; my cost was $212.

My Toyota pump started failing and was a bitch to diagnose as it was intermittent till it final gave out.
http://www.carpartswarehouse.com/addtocart/2005_Ford/Ranger/Fuel_Pump_Assembly/36-00606.html (Whole assembly)



http://www.partsgeek.com/gbproducts/MC/18104-07112601.html?utm_content=MC&utm_term=2004-2006+Ford+Ranger+Electric+Fuel+Pump+Airtex+E2535+04-06+Ford+Electric+Fuel+Pump+2005&fp=pp&gbm=a&utm_source=google&utm_medium=ff&utm_campaign=PartsGeek+Google+Base&gclid=CNqaivX84b8CFQSBaQodagUAxg (Pump and everything but the strainer)
 

Fill the tank with gas recently? Has there been any heavy rains lately?

Google to find out where your fuel pressure regulator is. My 4.6 was doing the same shit and I was getting ready to change the fuel pump. I changed the regulator and it has been fine since.

If you do need a fuel pump, and has the flex fuel 3.0, be careful. You have to make sure and get a flex fuel pump if you want to continue to run E85.

I had a similar situation where mine failed to restart. I've got an 05 with the 4.0. It seemed like it would struggle to start up at times and one  day it failed to restart. I was getting voltage at the plug but the pump wouldnt kick on. I swapped fuel pumps and the fuel filter and all was well.... For about a month.I hop in it one day and no start. Fortunately this time it was in my driveway. Turns out the inertia switch burnt up, like melted plastic burnt up causing intermittent no start. Unfortunately it didn't burn up the rest of the truck with it. While this was going on it had two codes but I don't remember what they were. Also be extreemly careful discomnecting those fuel lines. If you break those stupid fucking plastic clips you have to buy all new fuel lines, you can't just buy the 2 cent clip.

Look closely at the inertia switch. Ford put them in a great spot..........right where a passengers feet would be.
I've had numerous Rangers in the shop for this problem (Usually a voltage drop of more than 3 volts,sometimes just plain broken). Replace inertia switch and relocate behind the passenger side kick panel where it should have been all along.
It is internet diagnostics so without actually being there that is all i have for you at the moment. Good luck with it.

Which engine?

2.3
My son has a friend with essentially the same truck; his has shut off several times from the inertia switch. When I checked it, the plunger/button was "down"  I hadn't though about the voltage drop: the battery is like five or six years old (I looked at the date code and was surprised, but don't remember the exact date) Stop & go, start/stop/restart, A/C running full, well that would sap the amperage; migh well have dropped it too much, but it did spin over normally for quite a few more times, before dieing alltogehter.
Again, after getting it back home, recharging the battery over 12hrs it's run fine, even the 28 mile to work this morning running lights & Air, didn't fail.
I won't keep a vehicle I can't trust....I don't mind "toys" that constantly need attention after being played with, but the toy hauler must be reliable!

I've been running it along just fine for the last month or so, then it did it to me again: Ambient temp in the high 80's stop & go, stopped at the store, came out and it'll whip right over, but would not fire....sat there around a half hour and it fired right up like nothing ever happened. I was so pissed I could have dropped a flare in the tank. A week of back & forth to work (28 miles each way) and trips less than a mile with no problem.
It IS heat related, I think the engine was at or just below normal idle when shut off, just above 1/4 tank of fuel the last time, and around half the first failure. Again no fault found with the inertia switch, did act like it didn't have fuel or possibly no-spark.  I tend to believe its a fuel issue either from the pump or regulator, but don't want to start throwing expensive parts at only thinking that'll fix it.
I am searching for a replacement vehicle: nothing pisses me off more than machines that won't run or aren't reliable.

My 2001 did this for a while until I came back out of a store after about 5 minutes and it would just crank. The previous times I would just turn the ignition off for a minute and it would start. This time no-go. I reached up and punched the side of the plastic fuel tank, tried it again and it started. Bad fuel pump.

Could be a bad coil. Getting hot and causing a weak or no spark. When it cools it goes to working.