I if I were in your shoes...
I would probably stay with my current employer and try to increase my tenure and knowledge by switching roles to something with a higher pay level or to a position that could possibly fast track you or put you in a position of visibility. There is nothing wrong about actively seeking a better position outside of your current employer, but in the interim I would put in the extra effort to advance in the organization you are already in.
In terms of sales... Sales is all about confidence, strategy and product knowledge. If you are confident in yourself and your communication abilities you are ahead of the game already. Strategy will change depending on your target area, but once you have established a strategy or game plan you can take this knowledge and use it in any sales based position. All you will be doing is tweaking your personal strategy to fit the product and the buyer. Product Knowledge will come with experience. You can never know too much about your organization or it products/services. The one thing I stress, improvising on the spot is key, but never mislead the product/service you are selling. If you don't know the answer advise the client you will find out.
Good luck in whatever decision you make!