P0455 Evaporative Emission Control System Leak Detected (gross leak)
Means filling the tank should be easy, lol
So your issue with filling the tank is most likely a filler tube issue in a 1999 Ranger
1999 Should look like this:
https://images-na.ssl-images-amazon.com/images/I/61-+DIRejkL._AC_SY355_.jpg
So there is a larger pipe for filling, and a smaller Vent pipe to let the air out while filling
There are rubber hoses at the end of each so it can connect to the tank
If the air can't get out while gas is going in, then the pressure in the tank builds up and causes pump to click off
So my guess is that there is a problem with the filler, could be on filler pipe or vent pipe
Gross EVAP leak could be related if one on the rubber hoses has kinked and split, so leaking air
EVAP system uses engine vacuum to create slight negative pressure in the gas tank
So when you start the engine and start to drive the computer applies vacuum to the gas tank
Then stops vacuum and watches a pressure gauge to see if vacuum is holding, if it is not holding at all then "gross" leak
No gas cap would be a gross leak, lol
EVAP codes can't cause running issues, just not that kind of a system
Vapor lock can't happen on fuel injection systems because they run fuel pressure of 20 to 70psi, in a 1999 its 60psi
You could still have symptoms like a vapor lock, but wouldn't be fuel related, just heat related
With a 5.0l under the hood you could be building up too much heat in engine bay as outside temps warm up
This can effect connections and even coil packs as heat builds up
If you have an electric cooling fan you may need to have it running more to keep up engine bay air circulation to cool upper engine bay
You could just try running without the hood to see if "vapor lock" symptom goes away