I have a 2000 nissan maxima. Well this is what happens, I might drive it a bit agressive or in high heat and my car starts sticking in 2nd gear and does not want to go past that BUT if I shut off the car while I'm driving and restart the car the problems gone. This to me it feels like its a mechanical problem I just wanted to see if anyone else has had this problem with there 5th gen max. Because everyone tells me that the tranny is good so is the motor but noone can really figure out what the problem is unless its happening, can this maybe be a sensor going bad?

 

Its probably overheating, like you said this only happens in high heat.
Invest into an aftermarket transmission cooler. Try avoid pushing the trans too hard in heat, you will cook the clutches inside and it will cost you a lot to repair.