I recently did a transmission fluid change on my car and changed to Royal Purple, and experienced the same problem that many people did with the stiff shifting. So being I just dropped 40 dollars into there pockets for something that didn't work I decided I would give them a call and see what we could work out.

I ended up talking to a guy by the name of David Canitz who is a Mechanical Engineer for them. Through some research on both of our parts he came up with a possible fix for our shifting problems. This is a quote from our email conversation.

"I don't think it's a lube problem - I think it's inherent in this transmission that is more evident at low temps.
The fact that it's not a problem with the engine turned off but is with the engine running on initial startup leads me to one scenario where the clutch is not fully disengaging - which is keeping the input shaft of the transmission turning making for hard shifts.
If you have worn or moisture laden fluid - the hydraulics are going to be less than optimal - meaning it could be a contributing problem."

An Infiniti Service Rep has been quoted by another guy as saying that the clutch lines are too close to the exhaust. David's response was this.
"If the clutch lines are too close to the exhaust manifold - this would tend to heat the glycol fluid and then when it cools - it will tend to absorb water."

He also recommended that I try doing an adjustment to the clutch pedal height.

I'm curious if anyone has tried this already, and if they noticed a difference at all.

BTW after talking with David he sent me a case of 5W20 to try in the transmission. Here is his reasoning.
"If you installed the fluid more than 6 months ago - we've got a newer version of the MaxGear 75W90 that we can try or I would recommend going to our RP XPR 5w20.
This has the same oil film strength as the MaxGear 75W90 but is lighter in viscosity. An sea 75W90 is similar in fluid thickness to an SAE 10W40 motor oil."

I have changed back to the Infiniti tranny fluid and I am still noticing the stiff shifting, not as bad as with RP, but it is still there. I am probably going to try these two items on the next payday.

 

I was going to buy RP because it's available locally, but decided against it because of the stiffness and/or notchiness that some report. Waiting to see how the new fluid works.

 

I am going to hold off on installing the 5W20 until I do the next tranny fluid change. I don't want to waste the fluid I just put in there.

 

After reading many threads of which fluids to go with, no one has said any negative things about Amsoil. So with that said, i went and changed mine with Amsoil along with the differential fluid as well.

I agree with everyone who has used Amsoil, much better.

Look up Royal Purple and Redline for transmission fluids....and you'll find complaints. Go with either Amsoil or original OEM fluids.