Kinda a stupid question, maby? I was just going to use GL-6 rated gear oil 80W 90, in the diffs, D60 front, 80 rear. of my 2002 Ram. But a friend of mine said Dodge says use Synthetic oil only? Is that true?

I dont think you have to use synthetic but I would. If you put Amsoil in it you will get better gas mile's and you can leave it in for a lot longer then standard oil so it saves you money in the end. I run it in all my stuff even my lawn mower :)

The only place you need to run synthetic is in the tranny and t-case. Altho Im not sure about the t-case. But the tranny syncros require the synthetic, and if memory serves correct it requires the stuff that mopar sells. I goofed and put non-synth marine grade stuff and my 2nd gear syncro is gone now.

Look at your vehicle manual I think you will find dodge say's synthetic is a must. I even went to talk to the dealer about this and they said it would void the warranty if they knew synthetic wasn't being used (pricks)

Get Royal Purple gear lube. Use it front and rear as per your manual use the 75-140 in the rear if you tow. If your REALLY like your truck, change annually.

The manual does not say you have to run syn. It recommends if you pull a trailer a significant number a miles switch to syn.
I switched to mobil 1 and 5K later both pinion bearings went out.

The switch to syn was when they switched body styles. I never said all syn were good.Also says to change every 16000 miles if towing that could get expensive.