If there is 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 is 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 are replacing the dash in your truck, it's a good idea to go ahead and replace the heater core while you are in there. You will not want to do this job twice.