For a truly custom tune I would say Avalanche. I have had a lot of tuning over the years. Avalanche substantially changes the internals to tune for "you." They are in the US and have the process down to a science. Vorsprung basically send you parts which have some effect, but can not tune it to a high degree. They are in Canada which makes shipping long and expensive. Maybe they do great work if you send them your stuff. There are others like Flow and Dirtlabs also.
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