We just did a heater core on a 2001 Dodge Ram 1500, and yes it is a pain.
You will need to drop the steering column down and pull the air bag.
Then if that is not bad enough you need to pull the entire dash loose from the firewall and pull it. The heater core stands straight up with the inlet and outlet tubes having several bends that make it difficult to pull out I cut them off. The new one is no joy to put in as the box wants to be removed due to the bends in the tubes and lack of room to wiggle. just be patient it will take time and several different size of sockets and a t-25 torx bit.