There are a few reasons why the idle speed can increase, but it all comes down to the fact that you need to get that IP rebuilt, or get another pump. Your advance is probably shot, there could be wear in the governor or the metering valve, or their could be crap in the pump. It's unfortunate that your pump did not go the full 100,000 miles. Most likely that shop you dealt with did not replace some parts that should have been replaced.
Now I'll put on my moderators cap, and say that with regard to scary posts, please keep in mind 2 things.
1) These forum posts last forever, and can be read by anyone, anywhere, by a person who possesses little or no knowledge.
2) When you answer a question, it's always best to write it in a way that covers the widest audience.
What this means is, if you can't give the time to post a completely thorough response, then by all means, offer a worst case scenario. As an example. Someone says "my engine doesn't start", and you answer "use either". Now by providing that answer without any further education, you have just put yourself in a position to have a moral liability. Granted, when his glow plugs detonate his either and blows up his engine or causes him harm, your not going to be pulled into court, but you ought to feel some remorse for not saying "but make sure you disconnect all your glow plugs". So the correct answer is "do NOT use either". Now, if you take the time to give a complete lecture on the do's and do not's of using either, then that's fine. So when someone says your missing a throttle return spring, and your engine could run away, don't bash them for what you consider a "scare" tactic, because the reality is it could save someones life. If you go around saying "the spring on your throttle cable is all you need", then I don't want any advice from you, because when that throttle cable falls off and his engine is stuck at half throttle, I don't want to be reading when the post about him wrecking his truck comes around.
Always give the BEST answer if you don't have time to give ALL the answers.