Here is what you need to do...
Start with the truck stone cold, like after sitting overnight, remove the plug ontop of the radiator and remove the cap from the expansion tank.
Fill the radiator as full as you can and make sure that the truck is sitting level.
Start the engine and turn both heater ***** to HOT and set the fan to low.
Roll down the drivers window so that you cna keep a eye on the temp gauge.
Let the truck run until the upper raditator hose gets hot and coolant starts to come out of the hole in the radiator, once a steady stream of colant comes out replace the plug leaving the engine running the whole time.
Keep checking the temp gauge and sticking your hand inside the cabin to feel for heat.
Once a steady stream of steam starts coming out of the expansion tank replace the cap with the engine running.
Make sure that you keep the expansion tank full the whole time that you are doing this.
Full is covering the "X" in the bottom of the expansion tank.
Now drive it for a day, then let it sit overnight, the next moring check the coolant level in the expansion tank topping off as nessasary.
After you replace the radiator plug and steam is coming out of the expansion tank if you still do not have heat then rev the engine up to 2,000rpm and hold it for several minutes to force coolant through the heater core.
Let us know how it turns out for you.