I found it difficult to pass the AI at the Nurburgring, so I qualified my car in pole. The problem with qualifying in GT4 is that your out lap (i.e. the first lap out of the pits) isn't timed. Since the tyres on the FGT only last about a lap and a half at the Nurburgring, I had to do an extremely slow out lap, to preserve them. If you go out and crawl around the track on the out lap, aiming to start your qualifying lap with blue or just green tyres, you should be able to put in a quick time to sit on pole.
Are you trying to do the races in B Spec or A Spec? If you're doing them in B Spec, your driver might not be good enough (in which case you could try training him/her/it - guide here). If you're trying in A Spec then perhaps you just need a bit more practice (or you could try setting the car up more for each track, changing gear ratios etc)