Defogger Heater problems of the 2002 Nissan Altima

I have a 2002 Nissan Altima 2. 5 s I have had for less than 2 years. About 6 months ago at around 80k miles my engine started to randomly overheat even though coolant and fluid levels were correct. I had to tow it to a mechanic and he said the radiator was split. I spent $500 t replace that but then shortly after it happened again. We then replaced both thermostats on the vehicle and this helped for 2 months. Most recently we have been encountering a severe stuttering and shaking of the whole vehicle immediately upon starting it up. Regardless of it being in neutral, drive or reverse the car jerks back and forth very violently. After you drive it for a few minutes and the vehicle warms up it ceases this action. In addition to this though there is never any warm air coming out of the vents no matter how long the car is driven for. This is all happening simultaneously in addition to now the car is overheating all the way up but then jumps around so we never know where the temperature is at. Nissan themselves is very uncooperative in any capacity when attempting to rectify this situation. This is very disheartening as me and my wife are both working full time students and cannot afford to continue to chase this with time or money. My wife is a nanny part time and has had the car stop and need to be towed while she is out in the middle of the city with her 2 toddlers she watches. I am doing my best to avoid missing work as a result of having only one vehicle. We have a 2004 Volvo that has had no problems but this Altima is going to drag us down.

: the contact stated the vehicle would not start for two days. The check engine light was illuminated prior to the incident. The vehicle was taken to the service dealer, who was not able to duplicate the problem. Also the heater defroster was not working.