I have a 2007 Ford E450 superduty winnebago 31c, v10, dana 70, 4.56 gears nonlimited slip. I tow a 2002 Jeep Wrangler approx weight 3500lbs. The rear diff calls for 75w-90. I live in southern Idaho but tow mainly in hilly ares. Can anyone give me advice if it would be ok to run 75w-140 or would that be too thick. Thanks in advance