Land Rover Repair: 2001 Disco II - 52K miles, service engine soon light, proper tools

Question
My service engine soon light came on at 50K miles and the error code on diagnostic was P0734 - 4th gear incorrect ratio. My mechanic told me I had to bring it to Landrover but my experience with them has been terrible.
How urgent is this?
Are there any alternatives to bringing it to the dealer?

Answer
If it's not a LR specific diagnostic tool the codes read will not make sense, or read at all.  

There are many independent LR specialists that have the proper tools, and there are a few in the "hobbyist" price range that you can purchase to do your own diagnostics.  Namely Rovacom and AutoLogic.