World Class T5 fluid/oil Question

[JH96GT]

I'm swapping in the KC clutch tomorrow and have a question. Everything I've read says to use Dextron III ATF. When I bought it, it had 5w30 mobile 1 synthetic in it. (drained today).

Which should I go with? Shifting has been kinda hard at times, especially under hard driving (hitting 3rd, or downshifting to 2nd). Could this be a result of the 5w30?

Thanks.

 

[795.0pacecar]

Always use mercon dexron III or equivalent. I also dont like synthetic in a T5, it causes the carbon syncros to swell and wear quicker.