You're probably using a higher compression level (lower ratio). Remember, DVD Shrink is not simply ripping the DVD to your hard drive, it is reprocessing the video to compress it, this is very processor intensive.
You don't see anything about DMA in the FAQ? Are you kidding?
Same thing happened to me with a large flick.I rip't a 7.3 gb movie and it took about 50 minutes.But the strange thing was,I rip't another movie right after,much smaller(4.9 gb),and it took over an hour.I think it might have to do with the quality of the media in the movie itself.You know,done by the people who press the movie?I'm not for sure.But the 4.9 gb I did played fine.