09 newholland t6070 problem

[mccann1991]

HI
I am having problems with my 09 t6070 RC. When I start her most mornings she will go fine from C1-C5 but when she goes into C6/C7 she will have no power and will cut herself back to 1700/1800 rpm but half an hour later she will go back to normal and will have plenty of power and rev out 2000 rpm which she is normally like. could anyone help?

Thanks