i have a 03 ram with the same symtoms as your 03. but one thing that ive noticed is no one has mentioned if there is any smoke coming out the exhost. if there aint any smoke then ya cant be over fueling. no smoke means no fuel is getting in the cylinders at all and i hav no smoke on mine wile cranking so im thinking its electronic. mine also only happens when its blow 50 degrees out . eaither will start mine but it just takes a small shot and its up and runnin. i no it sounds like the air heaters aint working but a cummins with the common rail fuel system should start down to ten degrees but along with that my heaters work good. now there is a fuel heater in the filter housing . and it should be checked because the contenuety washers between the bands on a factory fuel heater crumble over time and get sent through your fuel system. i beleive this is what is causing trouble with most trucks of this age if it aint cought in time it can destroy injectors and pumps. i dont claim to no it all but ive been having this prob for going on three years and i left it go for a long time but ive been reading alot of posts and doing alot of research and tests on this prob so i figured i would share some of my info to maybe help some one out that has noticed other symtoms along with the ones i have mentioned

 

Hey Try ur intake heater it might be that check ur fueses and the relay for the intake heater!!!!