My husband has a 2014 Dodge Ram 1500., Hemi 5.7 liter. It has been showing some trouble codes. P2314, It is getting 9 miles to the gallon. He has replaced the plugs, coil boots,

Make sure that is the only code you are getting. If it is, then you may have a gas leak somewhere. I say this as, it is the only other logical explanation, as, your O2 sensors haven't coughed up a code. It is VERY possible your engine is not burning all of the gas being sprayed into the cylinder housing and it is going down your exhaust, then entering your catalytic converter and being burned off as excess. This will not give you an error code because your O2 sensors are burning off the extra gas, which means they are working properly.

I would verify all aspects of the engine firing when it is supposed to be( engines were much easier to work on when you had a distributor cap, distributor, etc... you could check your timing by simply loosening your distributor cap and giving it a small turn then hitting the accelerator and listening for any lag or latency, then you could turn it to where every time you just bumped the accelerator it would make the engine jump).

I know this is a lot of detailed info and, without being able to put my hands on it physically, puts us both at a handicap.

It is possible to have a diagnostics run via Auto Zone or Advanced Auto Parts and this may give you your answer. Personally, I think your timing is off( yes, this can occur even with EFI systems) and it needs to be observed and possibly reset\replaced.

Hope this helps.