Q: I was told I needed a new transmission. I am not sure if that is the problem.

If the transmission was always shifting smoothly, but only after purchasing fuel that day you immediately experienced reduced performance, I would first suspect (and try to rule out) bad gas. Excepting frankly easy to detect significant, and non intermittent, electrical faults in transmission controls, transmissions do not generally abruptly stop working. As far as what to do now, you can’t do anything until you get a specific, accurate diagnosis of what the underlying problem is. Telling someone "they need a transmission" is NOT a diagnostic and that is not information that is sufficiently specific to make an intelligent decision. If a specific fault was identified by a mechanic, or a specific component was condemned, based on actual testing, that is another matter. Transmissions involve hundreds of parts, not to mention external electrical controls, some of which are easily repaired or replaced while the transmission is on the vehicle. And, of course, the problem you are having may not be in the transmission at all but could be due to an engine management problem. To sum up, you should ask the mechanic to explain to you EXACTLY what is wrong with the transmission, where exactly means "what part", "what component", and so forth. Once you have that information, we can help you interpret it. If, by chance, the mechanic cannot give you any account of the problem, simply request a rough running diagnostic/poor acceleration from YourMechanic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.