From your description, it sounds like there's a problem with the CVT; it's probably going into "fail safe mode" due to possible overheating. However there are many other conditions in the CVT that could cause the CVT to drop into "fail safe mode"; the Transmission Control Module (TCM) sets this mode so that operation can be continued even if the signal circuit of the main electronically controlled input/output parts is damaged. One of the first things to do is perform an ECU/TCM code readout with a portable scan tool to see if any fault codes are set. The tool can be purchased at most auto parts stores. Post the actual codes here on the forum so that we may be able to help you further. If there is one or more fault codes set, they can help point to the malfunction. If you have a copy of the Factory Service Manual (FSM) for your vehicle, the code readout procedure is described there along with a listing of codes. You can download a copy of the FSM from this web site:
Owner's Manuals. The section TM is the one you need to read.
If the CVT only goes into "fail safe mode" when fully warmed up, then the suspected failing component may possibly be the fluid temperature sensor circuitry; this is just a guess, so the code readout is essential. Codes P17F0 and P17F1 never turn on the MIL on any Nissan model. P17F0 is the CVT "death code", it means severe belt slippage was detected.
The symptoms you describe seem to indicate judder. Judder will be most pronounced on a moderate to steep incline with light acceleration. Let off the gas at mid-hill, let the car coast momentarily down to 20~30 mph, then apply enough pedal to roll back up to speed. It should transition smoothly. If you feel any shuddering or surging, or the tach starts jumping around without pedal input, that's judder.
To enhance longevity, the CVT fluid should always be replaced every 30,000 mi. When the fluid stays in too long, the chemical properties of the fluid get compromised and it can no longer provide that cushion that's so needed between the steel belt and the cones. The fluid has two great enemies, and temperature is only one of them. The other is shearing force generated by normal operation of the belt, which increases on hills or with a load. This gradually breaks down and shortens the long-chain molecules that cushion the belt. You can generally deduce that by looking at the fluid; if it's very dark brown and has a burnt odor, it's shot!