I have a 98 ram 3500 4x4 v.10 and it started to overheat when my heater quit blowing hot air, it still blows cold a/c but no heat. I have flushed my radiator twice replaced all hoses twice replaced thermo's twice and fan clutch once and no luck. Could the trans be making it over heat I noticed along time ago I was pulling a boat down to the KEYS (I live in florida) that while I was pulling the a/c would cut in and out. Could my trans be going bad in wich case it is making my motor overheat

Several thoughts:
1. Only use 50/50 mixture of antifreeze and distilled water. Positively no tap water, well water, or softened water. You may need to replace the radiator and/or heater core, due to mineral buildup. Feel radiator surfaces, when the engine is hot, and see if it gives you any clues.
2. Install an auxiliary transmission cooler--a must on any vehicle used for towing.
3. Use full-synthetic ATF (such as Amsoil Universal Synthetic ATF)--transmissions run 50 degrees Fahrenheit cooler, shift better, get better gas mileage, and last longer. Change ATF and filter at recommended intervals.

I have the same problem with my 2000 dodge 1500 4x4. Before mine overheats the heater starts blowing cold air. I haven't replaced anything yet, what should I start with?