autobox 3rd gear issue

Have an issue with 3rd gear selection on my disco 2 td5! it changes late and when she's all warmed up, all other gear changes seem ok.
1st to 2nd all fine but 3rd isn't changing until 30mph when previously if not under throttle would change earlier!
no signs of fluid leaks but due for fluid change in about 10k
Any ideas?
Paul.

Mine doesn't do third till 30+ mph

My old TD5 was slightly higher geared due to tyres (265/75/16)
This is what mine did;
Changed from 1st -2nd 15mph
2nd - 3rd 29mph
3rd to 4th 40mph
4th gear torque converter locked about 55mph

HTH.