I have been using Castrol GTX but not for any specific reason just wondering what you guys use...... also 5w-30 or 10w-30

Mobil 1 synthetic in engine and differentials.......change it every 3000 miles. (engine)
I also use Purolator filters now.

Royal Purple in my engine and front and rear diff. I am using the Purolator Premium line I forgot what they are called filters on my truck. I had been changing the oil about every 3k miles but have let it go almost 5k now and am planning on letting it go to 5 as It's just too expensive to keep doing it every 3k although I may go back to it after this time. On my 06 Honda I use RP with Honda filters, on my Chevy I used Mobil 1 Synthetic only because they were sold out of RP (most likely will use RP next time) with I think I used a AC Delco filter, and in my 96 Honda I use RP with K&N filters.

Pennzoil 10w-40, it works and for filter i use FRAM...

Quaker State 10W 40 filter Fram.

Valvoline Max-Life synthetic

None of the above ... Castrol Syntec 5w50.

I use Mobil 1 5W-30 hey every how many miles do you change your differential oil?

How many miles do > I < change my differential oil? Never. However, I believe Dodge recommends 15,000 miles ... not sure.

Valvoline Max Life 10W-30 from November through April
Valvoline Blue 15W-40 during the summer (even though I have a gas engine)
Valvoline 75W-140 Synthetic in the diffs w/ BG limited slip additive

Been using the same fluids from day one.