I may be a bit late here replying: new to the forum, but I am a professional wheel builder by trade (In the UK).
You will always have alternating spokes at different tensions, if you do not pay due attention to the building process.
Why? because you have one spoke with the head "in" (the flange) and one with head "out".
The "head in" spokes take a shorter distance to the rim than the "head out" spokes. These have to go through the hub, over the flange and then inwards to the center of the rim. Taking a longer distance, thus putting higher tension on the same length spoke.
When you are building your wheels, put an extra turn on the head out spokes before you fully tension the wheel. This will solve the issue and bring your tension variance much closer.
If you have a good wheel builder locally they WILL be using a tension meter. This tells you how tight the spokes are. Using a spanner or piano tuner does NOT work (yes, I tried!). I use a DT Swiss tensio digital (blue) and the analogue (red). The park tension meter is OK for a budget tool.
If you have your wheels tensioned accurately then they will last longer and not need retruing unless you bend the rim.
Hope this helps