My Auto gearbox not changing properly, it holding 1st until 4000 rmp

Hi can anyone offer advice.

I have a td5 diesel year 1999, the first gear holds until 4000rmp the gearbox changes smoothly but the gaps don't appear to be right.

Cheers in advance

as with any auto problem check colour and smell of oil by draing a cupfull out when cold ,that little wont hurt box ,then get codes read ,getting your own hawkeye or similar diagnostic kit for a few hundred pounds will save you money in long run,even if your unsure of using it theres people here know