Throttle Position Sensor on a Diesel truck

Hi everyone.

Here's yet another question about a diesel truck. I've looked over the truck forums and they are not as helpful as FABO. Imagine that.

Anyway, 98 Dodge 2500 24 valve truck that's close to me I want to look at, the guy says it needs a throttle position sensor. He doesn't say why he knows this. Is this a straight forward repair, easy or tough, expensive? It's priced cheap, probably will be sold before I call him. I just wanted to get a heads up on what a TPS entails.

Anything else I should look out for? Is the 24 valve engine a good one generally? Thanks everyone.