Gear Oil - Synthetic or Not?

As the title states, I am wondering about using synthetic gear oil in my axles.

I have used Valvoline synthetic gear oil for many years and several hundred thousand miles in other trucks with absolutely no issues. I have no hesitations about using it.

However, I had East Coast Gear Supply (ECGS) build my differentials with 4.56 gears, and they recommend not using synthetic. They recommend Lucas gear oil. I know Lucas is good oil (and a lot less expensive than synthetic.) I asked them why their recommendation was non-synthetic, but did not get a satisfactory answer.

I am getting ready to change the axle oil, and am wondering if I should switch to synthetic.

Any thoughts and/or experiences, good or bad?

 

Not sure about your set up but I installed Lucas 75w90 Synthetic in my STOCK diff. I will be doing the t-case and front diff soon.