Go with an OEM infiniti/nissan TPS sensor. I learnt that lesson years ago on my GXE when I bought a borg-warner TPS sensor only to worsen the problem.. Going OEM fixed the issue.. same thing..transmission abnormal shifting..
If you feel adventurous, check this site out:
http://www.cardomain.com/ride/748507/6
It has a TPS disassembled which is identical enough with the J30 unit... I would order a nissan spare and then take the risk of disassmebling the old one if you are going this route.. Regardless..good luck