Hard cold start 2003 dodge ram diesel

You don't say whether it is petrol or diesel engined or whether the engine is cranking fine but won't fire.

Certainly an engine must crank quick enough but even then if it is the best diesel engine ever made it is unlikely to start below freezing without an artificial starting aid. Such an aid is already installed but must be in good condition. Heater plugs do fail sometimes or get tired and lazy so they need checking and sometimes the timer relay fails to switch them on. Good injector spray patterns are also needed for good starting.

Petrol engines need enrichment of the fuel/air mixture for cold starting and a very good spark at the plugs. Worn spark plugs is the most common cause of poor starting and if the ECU isn't getting the right information about temperature it will be unable to make the correct fuel adjustments.
A good injector spray pattern is also important.

Lots to think about...

I am going to assume ( dangerous) that you have a diesel. If the grid heater is working it is not advisable to use starting fluid because it can combust in the intake manifold. However, if the intake heater was working, you will not have any starting problems above 0F. I would check your grid heater for power and continuity. There could be a fuel delivery issue,but starting fluid usually does not fix that.

check for water in the fuel filters and drain them accordingly also check the fuel heater circuit in the fuel filter hosuing to make sure it is working and not shorted check the glow plug relay to mae sure its functioning correctly also

You don't say if you plug it in, but this really really helps.

sounds like glow plugs or primary injectors

your glow plugs not working or glow plug relay or controller not working.

your glows plugs not working. check glow plug relay or fuse.

time to have the injectors replace and calibrated by an accredited diesel specialist shop
indicates squirting and not atomizing

The lift pump is bad Check the fuel pressure with a test gauge.

when you start the truck do your lights dim and your volt gauge fluctuate. if they do, i would think the grid heaters are working. could be an injector going out