Welcome to Fluther.
“Gear noise” is an entirely useless description of the problem – if there really is a problem. The fact that your transmission shifts early (or late, it’s not clear) is a more specific issue, again “if it is a problem”. Does the transmission run hot? What is your fuel consumption like? And is this a recent development?
“Spending money on a mechanic” is no criterion for anything. What did the mechanic do?
When the oil was changed, was the old oil “flushed” or merely drained?
Additional information would also be helpful if anyone is going to diagnose and offer resolution to what you see as a problem: How many miles or kilometers are on the odometer? Has the transmission been rebuilt at some time? Has it been disassembled at any time by an amateur? Has the vehicle suffered any other relevant damage?