Looking good! I like the thumbs up half way through.
I've been playing with the air seat on mine and it feels like I have mine around 1.5"-2" mark. My seats all the way back and I haven't noticed any vibration. Could the wire harness be against something possibly or a rubber damper either under the seat pan or one of the big ones as part of the seat suspension be out of place, missing, or the through bolt on the suspension rubber be touching metal?
I tell you it's almost stupid how excited after 12 plus years I am to mow now. I also want to throw my gps on and see what speed it's really running. My Super Zs did around 15 mph and this thing feels pretty darn close by the seat of the pants. TLS caught these 400s are running the ZT-5400 hydros which are the same as the two speed Cheetahs and Husky PZ6034FXZT two speeds. I think I'm making my ROPs disappear tonight along with my first oil change at about 7 hrs.
I wrote a sort of review here http://www.lawnsite.com/showthread.php?t=379728
Gravely also has a sticky thread on owner feed back on their products which you should hit. I think it's great.