Well 1st, If your Pre load is adjusted (Check it as they loosen up very often all by themselves.)
2nd, yea It can be the Spring alone. A lot of people including me have installed a Progressive spring. Do a search on poor mans spring tool.
This spring does work wonders and is a inexpensive fix for your problem. If money is no object then hop on Tricky Air's next sale and so Air spring.
I know someone who did and might have a Spring for sale, he'll PM you maybe. But I know he has only about 3K miles on the spring. I have about10K on mine, two up, Fully loaded for a week, and this is what we weigh in at like that, And I mean packed to the gills.
I did call Progressive spring who said use of this spring on the stock shock is not cool, but, I'll go with the group here and say yea it is. I had some issues but it wasn't what I thought or what Progressive said it was. The shock will work wonders for ya. one and two up.
It is shorter and will drop the bike, they say 1" I found that to be about right but if you adjust pre load to MAX (2"

you will be better than now and since it is "Progressive" It will get stronger as it is compressed and bottom out much less if ever.
Can you do it yourself is a loaded question, Many have done it themselves, the poor mans spring tool works great. You'll need normal shop tools found in a shade-tree mechanics lineup. Some tools in the bikes bag can also be put to use.
It's always

cheaper to buy what you need and DIY than pay some rip off to do it wrong for you. And this even figures in a few major screw ups

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