#1. on the 5.9 and 5.2 they both require 5 gallons of antifreeze, make sure if you've flushed the system there is 5 gallons or 20 quarts.
#2. If your over 100k check the following, waterpump, radiator, thermostat, lines and leaks! Ensure there is no coolant in your oil, around your inside oil cap or under the valve covers. Very important you do not have a head gasket issue.
#3. Check to ensure you do not need a headgasket on either bank 1 or 2.
#4. If you've changed everything and are still experiencing no heat or little luke warm heat do the following:
most likely there is air in the system if your heater core is gurgling when you push the gas in fast acceleration. If this is the case you'll hear it in the cab.
#5 Low antifreeze with cause this, and no there is not a bleeder valve on either system for these trucks.
#6. QUICK FIX: cut the bank 1 heater core line about 1 foot before the intake back to the water pump.
#7. Buy a brass 3 way shut off valve with 3 brass 1/2 inch to 5/8 inch fittings. Put on teflon tape, and thread the fittings onto the valve. You will need to buy this valve most likely on line or at a specialty plumbing store.
#8. add some 5/8 heater pipe to the bypass ( or up valve). Attach it to a 1/2 gallon funnel.
# 9 Fill the funnel with coolant, start the truck, shut the valve so that the new coolant will be sucked into the water pump, make sure it does not exceed 5 gallons or 20 quarts. Turn the valve back to open, remove the extension to the funnel, problem solved. Turn up your heat and it should be very hot when the truck comes up to temp. You have just drove all of the antifreeze into the system. You also now have a air control valve on your sytem for future needs and you will most likely solve your heater core problem.
#10. This is the trick if you've flushed, changed the thermostat, hear gurgling or it just did not take the 5 gallons of antifreeze. Most people will tell you it only took 3.5 gallons, well there is your problem, these trucks are great until you need to add coolant. Even burping the system is a bitch. This is the way to force in the antifreeze and force it to belch all at once while destroying your cold cabin problems.
#11. If you have not tried all of the following there is a youtube video of a guy in canada that did a similar thing as I described however this way:
My way as explained is a sure proof, much easier, fast way to fix this problem after you've flushed the heater core, added a new radiator and water pump and just do not want to rip out your dash, when in the long run it is low on coolant and you have to force feed it in!! This is the 99.9% reason for almost all of the dodges I've seen. Make it drink the coolant, you should not have to burp it like a 3 month old. You would think the designers would build the system this way from the beginning but hey thats why they are engineers and not mechanics!! Cheers to all I hope this helps.