1999 tacoma manual transmission gear oil

After changing gear oil .Truck shifted a a little rougher.
Went on line to find the cause and read nothing that could help with a solution.
Lots of talk.
So called toyota corp and told them about problem and that I installed synthetic 75w90 gear oil. Their response was to drain synthetic out as soon as possible and put in conventicle gear oil,which I did.
Shifting now back to normal.
So if anybody plans on trans gear oil change,make sure to use conventional gear oil.

 

Toyota is probably right. But here is what I did, after checking with Royal Purple; At 122K I went to all Royal Purple fluids, and Royal Purple "Synchromax" in my 5 speed. It's full synthetic. Truck's now at 126K and couldn't be happier! Just sayin'.