I had a gogo manifold on my old truck and I was happy with it. My spool up was noticeably better and my egts @ WOT dropped about 200 degrees. Never did a before and after dyno but it did seem to add some SOTP power.
I have a GoGo intake on my truck but its currently in the shop so nothing I can report on. Doug said it will be very noticeable of a difference between it and a stocker though so I'm stoked to try it out haha.