I don't own a 3rd gen, so take this for what it's worth, but I agree with the above. Your shock might be too long and has no "up" travel, there by reducing your overall wheel travel. It looks like your not even going to get into your bump but about a 1/2" before your shock fully compresses. Your ride height looks pretty good, so maybe your springs are where you need them, but also like mentioned above, if you didn't upgrade your springs, all that shock travel won't do you any good. It also looks like your lower link will contact the reservoir on full compression of the shock. I would say any 4 link set up like this needs almost as much "up" travel as "down".
Here is a link to my custom length 4th gen I built with some shared knowledge from some of the Cali members. It cycles pretty well but it still needs more "up" travel, the back end still gets a little bucky which ain't fun at 40 to 60 mph.
https://www.youtube.com/watch?v=OoJUF02t4bo&feature=youtu.be&t=60
Hopefully someone with more than my limited knowledge will post up and help you out.
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1988 DLX 22RE AUTO BLACK-
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2003 SR5 SPORT V8- Build-
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