iTunes & iPod -- Mp3 File Recognition and Playback Problems

Situation:

I own a 30 GB Photo iPod (purchased in January '06). I communicate
with it using iTunes 6.0.5.20. I run all this using a PC with a
Windows XP OS.

I've been converting a series of pre-recorded lectures from audio tape
to Mp3 digital format using Audio Cleaning Lab 11 (Magix).

The resulting Mp3 files play normally using Windows Media Player
10.00.00.4036 -- Each file plays out to the end, and its duration is
properly recorded.

However, when I take these Mp3 files, import them into iTunes, and
then export them to my iPod, I experience the following problems...

Problem 1: For some of these Mp3 formatted lecture files, both iTunes
and my iPod abruptly end playing the file before the file has actually
concluded and then switches on to the next file.

Problem 2: Also, iTunes and iPod do not properly record the times for
the files. Each file is roughly 45 minutes long. Yet iTunes/iPod
shows them (incorrectly) as being anywhere from 39 minutes to 58
minutes in length.

Attempted Solutions:

I've tried clearing the Mp3 files from my iTunes and my iPod, and then
re-importing them to iTunes and exporting them to my iPod. However,
both the problems specified above persist.

Question:

How do I get iTunes and my iPod to deal with these Mp3 files so that...
a) They will play out to the end of the file before switching to the
next file, and,
b) They will recognize the duration of the files correctly?

Thanks,

2privatus@comcast.net