Gear Shift 3rd to 4th

[dwahi]

Hi All

So now my 280SL has begin changing at a slightly higher 3000rpm from 3rd to 4th. It was fine until yesterday changing all gears at 2500rpm. Has anyone else had the issue..its strange that 2nd to 3rd is at 2500rpm and 3rd to 4th is 3000rpm? The change is smooth, but just little perplexing.

Thanks

DAvid