I own a 2013 JX35. Purchased in July 2013 with a May 2013 build date. Based on reading the JX35/Pathfinder forums, Nissan/Infiniti transitioned the 2013 JX35s to the Pathfinder version of the CVT some time in early 2013. So, initial build JX35s had the CVT that did not "shudder", while later builds received the same CVT as the Pathfinder.
I have just under 5,000 miles on the JX at this point. I have experienced "shudders"--particularly during low speed city driving-- but they have lessened as the JX accumulates miles.
This is my third Infiniti (98 I30, 11 FX35), with the other two being rock solid during ownership. I'm a bit disappointed by the JX. Have also experienced several other minor build quality issues, especially the one where the roof molding comes apart near the front windshield. I mentioned this during my last service visit in February -- to date, the new part is still being "ordered". There is also a passenger air bag software recall pending on the car.
I do not expect to keep this vehicle past warranty -- will most likely trade for a MDX in the next year or two.
P.S. Also, the JX35/QX60 likely has the same VQ35DE engine (265 HP) that your wife's earlier G35X had. There is also a VQ35HR variant (303 HP) that is used on the EX/FX SUVs.