Last winter I bought a 97 Ram 1500 4x4 (54,000 miles from a good friend who bought it new) and the heat was really not hot. I had the heater core back flushed and it helped a lot but I think the core will really need to be replaced before this winter.

Flush the core BOTH ways (a lot of crap came out of mine) and make sure the flapper door is operating properly.