Not sure if this is common or something that can be remedied. When boat starts to get into the mid 70's it starts to get unsettled and starts rocking side to side. At this speed tabs are level and trim is around 5-6. It gets bad enough it's concerning to point I usually get out of the throttle. Props spin in and are 25p mirage plus.

I don't quite have the same setup, running 5blade 28p, but I get what you're saying when I power up into the mid 70's quickly and start trimming the drives up I also get the chine walk. If I take it slow from 70 and gradually trim the drives up, 1 level at a time, I have no problem getting 80+. Also helps when the boat is balanced so you aren't playing with the tabs at that speed.

How do you like the 5 blades?

They came with the boat, supposedly custom made by Throttle Up, but they are by far the best prop I've ever had on the boat. I've tested Bravo 28's and 30's, about to test labbed 28's, but nothing has compared yet. I'm running faster at lower rpms at every point with the 5, also a higher top end without hitting rev limiter.

I also have whippled 377's, so the 5 blades handle differently for me than they would for a stock 377.

Google - Chine Walk.

Trim the drive in....and adjust tabs accordingly. Look into the weight distribution of the boat. Verify that the steering system is bled and you have no "slop" in the wheel.

Remember - sometimes you can come out of the throttle and make it disappear but you can NEVER throttle through it..only gets worse.

Isn't 5-6 on the trim a bit much ??

5-6 trim isn't unreasonable on the 28zx. I usually run around 4-5 myself, any higher and she starts walking on me unless I'm alone on the lake/river. I suppose I can trim her up to 8-9 and see more speed potentially, but I bought the boat to enjoy, not to bury me 6' under.