2002 ranger edge 3.0 I've had these codes ever since I've had the truck. Would these leaks cause reduced mpg at all?

 

No, wouldn't effect engine operation, but could effect MPG because gasoline is leaking out of the gas tank

P0455 Evaporative Emission Control System Leak Detected (gross leak)
P0457 Evaporative Emission Control System Leak Detected (even bigger than gross leak)

EVAP system uses engine vacuum to pull gasoline vapors from the gas tank to prevent these vapors from polluting the air while driving when gas is sloshing around in the tank
Then when vehicle is off residual vacuum pulls any fumes thru a charcoal filter/canister

Your codes mean the gas tank can not hold negative pressure(vacuum), and not even a little pressure, lol, "big leak", like no gas cap

Common reason for these codes is No Gas Cap, or the Filler hose/Vent hose has rotted out, so cracked, this can allow gasoline to spill out when driving and fuel is sloshing around, so lowers MPG


The gasoline fumes from the tank are burned in the engine so, in theory, if these fumes are just being released into the air then they are LOST and not used to move the vehicle forward, so that would effect MPG, especially in warmer climates where there are more fumes in the tank with warmer gasoline
But I doubt this would even be noticeable, but it WILL effect MPG, for sure
The spilling of the gasoline from a "gross leak" would cause a noticeable effect on MPG

 

As RonD said about gas cap or vent line. I had the P0455 on my Nissan and ended up having a cracked plastic line. So do yourself a favor if its not the gas cap, inspect the lines and connections of the vent line really well, it can be difficult to find.

 

I replaced the gas cap weeks ago but code came back. Only real thing I can do is pull off the bed. Do you know the correct size bolts for the bed and is that all there is to removing the bed? Also don't see any cracks in fuel filler hose

 

I took the bed off don't see any cracked houses. But found what looks like bite marks on a wire cover. Also he thinks it could be the canister vent solenoid. idk just the wire cover was chewed that was connected to the vent solenoid.