You asking for a guess at many questions-no one can do that

You need the car in a shop & pay for diagnostic time, to answer
those questions, once any problem is found

Why would someone tell you anything ?
Were they working on finding answers ?

Have you not checked for codes or done any testing of the fuel system,
checked for spark or mechanical timing,etc,checked oil & trans fluids,
dead battery !!

May be time to let it go to car heaven & get something newer,after you pay
for a couple hours of testing of the car

There are numerous possibilities and it is unlikely that you have a transmission problem from the description given. Like Teddy said, a visit to the shop is necessary.