What weight gear oil

2015 TRD Sport DC LB with v6. Was wondering what weight gear oil to use in the diffs. I've seen the tutorials that specify

$30 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75W-90 for both diffs but I've always used 75W-140 in the diffs of my previous trucks, both Dodge Dakotas. Any opinions on what's best? I do live in Southwest VA so the temps vary from a low of 20 Degrees in the winter and high in the 90's in the mid summer. And I don't tow very much but do use my bed for the occasional load of soil or mulch. Thx >>AJ

 

my manual recs 75w85 GL5 I used Redline brand was the most reasonable price on that weight I could find, its a very thin oil compared to Mobil1 75w90, most people use Valvoline 75w90 full synthetic which has the closest viscosity index to the 75w85 gear oil that I have found, I will probably be using the Valvoline on my next 90k maintainence due to its price and availability

 

Thx Mush Mouse. I appreciate your reply. Reason I like Mobil 1 is they include LSD additive. Not sure I need it in the 2015 diff but can't hurt. I always thought Redline was more expensive. I believe one good reason to stick with

$30 75W-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75W-90 is the transfer case requires this weight gear oil.

 

i just changed both diffs and the transfer case with

$30 75w-90 Synthetic Gear Lube - 1 Quart (Pack of 2)

75w-90 Mobil 1. i'm at 47,000 miles and i changed the oil the first time at 20,000. the front diff and transfer case were pretty clean. rear diff was dark but not concerning. both magnets had collected some metal.

 

I'm running 75-110 Amsoil severe gear in my front and rear diffs on my 2004. No problems yet. I also have Amsoil in the tranny and transfer case. It should at least double or triple my change intervals unless I drive through creeks all the time 2 ft. deep which I don't. My thought is that I live in the mountains and constantly am going up and down grades. It gets down to around -15 here and I haven't noticed any "gear noises" even at that temp. The 5 speed manual is notchy and sometimes hard to shift at first when it gets below 0 but it smooths out pretty quick. The 110 viscosity isn't going to come into play unless the diffs get really hot. I also run Amsoil Signature 10-30 in the engine and am now going 8500 miles between changes with oil analysis done.

No, I am NOT an Amsoil dealer nor am I trying to sell the stuff. I just saw the results of using Amsoil in another car I owned 20 years ago. If I own a vehicle that doesn't use oil I'll always run Amsoil. They invented synthetic back in the 70's.