Let’s stop and back up a bit, okay. You have put so much into your note, my head is spinning, but I will give it a try.
First, your instincts are right. It’s time to say sayonara to your mechanic. I am not saying anything bad about him. I am just saying that he isn’t a good fit for you. You need someone who is more empathetic to you and your needs and your income.
What you need is what is called a “safety check.” This type of check tells you if your car is safe to drive and it helps to indentify where the problems are. It should cost you in the vicinity of $125. I know that your money’s tight, but I think you’ll be better off for it.
You get your safety at your local Nissan dealer. Yes, I am telling you to go back to the dealer, but there is a reason for it. With all of the stuff you have been told about what’s wrong (I honestly still can’t figure out where the transmission part of it comes in, though paper-on-paper indicates that you might have a band problem as it might be slipping bands/clutches — this is just a hunch) and all of the contradictory advice you are receiving, the dealership is the only place where you will find a good starting point.
Notice that I said starting point because once you have received your safety, I would advise you to check with your local AAA chapter. A few years ago, AAA began a program that approves repair shops, giving them the AAA-approved logo. Because they have the AAA-approved stamp, they have to meet certain requirements mandated by AAA. They are more consumer-oriented and up front in dealing with you. Right now, you need someone in your corner and I think you should look into this program to find a good match. They should work with you to get your Nissan’s problems solved.
As to your specific problems, forget them for the moment and concentrate on an overall health check of your vehicle. Then, take it to an approved repair shop and have them look it over. Ask them to work with you in setting up a service plan to get your Altima’s problems solved.
Transmission-wise, if your Nissan is still moving briskly and not juddering or dropping out of gear suddenly, then I wouldn’t worry about issues just yet. Hold off on the transmission fluid flush for the moment. It could cause more harm than you know as it is done under pressure and it could cause things to be loosened and the loosened things can become lodged in places they shouldn’t be, causing more harm than good.
One more thing, have the technican at the dealer do a read of the engine control computer (ECC) memory for error codes. You mentioned that the check engine light came on and then went off. That indicates the ECC caught a code from a component. That very code may solve all your problems or at least start the solution.
Please let me know what happens.