I used to be a fishing guide up in Alaska. I shipped a ton of fishing gear, and fish back and forth. I used Alaska Air Cargo to ship my gear. The best way to do it is to call ahead, to Alaska Air Cargo (the one I used was at SeaTac) and tell them that you are coming by and when your flight is or when your planning on picking your stuff up in Anchorage. Then the day before your flight you drop all your stuff off at Alaska Air Cargo and pay them. Your stuff flys up on a freight plane overnight, if there was a freight plane scheduled, and you need to pick it up at the location when you get to your destination.
At SeaTac Alaska Air Cargo is on air cargo road, and in Anchorage I forget what its called but its like right across a parking lot from the airport less than a block away. If you called up Alaska Air Cargo I'm sure they could tell you what you need to do. Also make sure that they have a freight plane scheduled to fly up between when you drop your stuff off and need to pick it up.
I believe this is about 1/4 what it costs to check additional bags and there was no maximum weight.
Good luck!