Diff Fluid too Thick?

I changed the transmission fluid (and front diff) recently in my 1997 Sambar 5 speed. I used SEA 140 (GL-4). Seems a little sluggish when first driving. Almost like the parking brake is slightly on. Is it possible that the 140 is too thick? If so, opinions on if this will damage anything inside.

 

140 is too thick. The fluids called for by Subaru is 75W90 or 85W90.

 

Thank you @rkrenicki
Well, another change is in order in the near future.