I have Nissan Altima 96, automatic, 75000 miles for almost 5 years. It started to have problem with gear shifting. At about 60mph on highways, it sometimes vibrates. I don't know much about the car but my colleague who went for a ride with me said the gear didn't shift down correctly. The engine starts to vibrate and make really loud noise. I have to slow down and go around 40mph for a few minutes and the vibration and noise is gone.
Now I just used back roads to commute to work and the car runs OK. I took the car to two machenics but they didn't really drive on highways and couldn't hear the noise. One of the mechenics said that my car didn't rally shift correctly even in the lower gear. I did change the transmission fluid and filter but it didn't help.
Should I forget his car and trade in for a newer car or have it replaced with a used transmission. How much value will I get with trade-in? Or should I try with a used transmission. If I want to keep this car for a few more months by driving back roads, would it possibly make things worse?
Any suggestions?
thank you.