starting problems?.

[AudiB5S4]

Hi there,i was wondering if anyone could help me my car is a 1999 audi s4 b5 the car does need pressure testing as it drops off boost at 4000rpm,it also has a brand new bosch battery but when the car is warm or hot it seems to struggle more than if it is from cold im thinking it is the starter motor but not too sure,any help would be much appreciated,kind regards shane.