You should find that the ILI9481, R61581, ILI9486/8 all behave slightly differently with User command 0x36.
Compare the datasheets for Bit #0, #1 in the argument (i.e. FLIP_GS, FLIP_SS)
Of course there are tens of other 320x480 controllers that might appear on the Ebay market.
You need to test Manufacturer commands for further diagnosis.
Not only controllers that differ. The physical TFT panel varies too. e.g. directions, colour inversion, ...
Remember that this is Mr Karlsen's library. I have no intention of hacking it. Just offering advice.
David.