temp gauge

[camturbo]

Hi all my temp gauge used to read dead on 90 but gradually recently its begun to slowly to move slowly back to its starting point. After a 50 mile drive its hardly moved. Header tank is on max and I have hot air still as well. Am I right in thinking its the cts that's at fault? Had a new water pump and thermostat fitted last year any ideas? I did fit a new cts last year as well but think I got it off ebay.
1.8t 1999 apu
Cheers