Sandisk Clip Sport audiobook problem

One large file does work on the Clip+ and Zip but it’s not so good on the Sport and Jam. It becomes almost impossible to fast forward on these players on large files. I actually do the opposite as if I have an Audio book as one file I use a freeware programme to slit it into parts as I find it easier to navigate etc and these slpit files seem to behave themselves on my Sport as I have no problems with the order getting confused. I never use any tags as they just seem to make things more complicated.