Can you see the problem of transmission just by driving?

Hello,

I just reaplced my transmission. The mechanic drove the car and told me that that transmission needs replacement. Is this possible? Or do you actually need to take apart the transmission first to see the problem? Did I suckered into replacing my transmission when the problem could have been a minor?
The reason I took my car to an mechanic was because it was shifting REALLY hard in every gear.

Well, taking the transmission apart means you are already done most of the work for a rebuild so you may as well finish the rebuild.

Most transmission problems can be diagnosed by a test drive, fluid inspection and analysis, visual inspection, electrical or computer test (for newer cars only) and a hydraulic pressure test. Usually, the only actual disassembly that is helpful is to remove the oil pan and filter at the bottom of the transmission, (about a 15 minute operation)

As a transmission rebuild is expensive, it is always a good idea to get another mechanic's opinion about the problem before spending any money. Depending on the vehicle, some harsh shifting problems MIGHT (but not always) be repaired without a rebuild.

I wouldn't say the mechanic 'suckered' you in to an expensive replacement. It is possible they did not know for sure how to diagnose or fix the problem without a replacement.