I hear about these tranny problems here and my 350z and I was wondering is it always a grinding problem at a high rpm between shifts?

No thats not normal take your car to your dealer. We've replaced 4 or 5 trans for that problem

ive had mine replaced twice. it grinds between 2-3 shifts or 4-5 shifts. so 3rd or 5th grind. its a loud grind and u can feel it in the shift ****

Is it more like pressure to get it into the gear or you can actually a grind feel and noise?

Mine committed suicide at 18K miles. 4th-6th gear syncros went. Started with a little grind, but within a 1K miles of that the car wouldn't even engage those gears. Was hell getting it warranted but all worked well in the end. Got a new clutch out of it also.