If you plan on doing a lot of work on your rig yourself over the lifespan of your truck, buying an OBDII reader is a good investment. They're usually around $200, although you can probably sniff out a deal somewhere.
If not, AutoZone will read your codes for free. Just make sure to write down the number itself---they'll offer you a diagnosis, but my experience has been they match the codes for a Ford or Dodge, not a Rover.
Yeah, it's under the steering column for a DI.. can't miss it.