I have a black 5 generation 120 gb ipod classic.

i have a black 5 generation 120 gb ipod classic. in long (2h35min) podcasts it would usualy skip the remaining 30 mins of program. Recently i also discoverd that a specific song(which once the ipod is connected to itunes plays the same son perfectly) wont play on my ipod when i'm in the gym. it skips it and goes to the next. ive already tried deleting it and replacing it again, but no luck.