If there's coolant on the passenger side floor of your '94-'02 Dodge Ram or if the heat is not as warm as it should be, it's probably time to replace the heater core.
Replacing it is a big job, but a do-it-yourselfer with the time, tools and a factory service manual should be able to do it. Set a day aside and save a lot of money compared to having a shop do it for you. You'll find a number of videos on YouTube demonstrating how to replace the heater core if you want to have a look before attempting this job.
If you're replacing the dash in your truck, it's a good idea to go ahead and replace the heater core while you're in there. You won't want to do this job twice.
NOTE: This part is OEM and different than what you will find at your local auto parts store. The tubes coming out of the OEM core do not have swivels in them and will take a bit more effort for installation.