I took a ride in a friends ZT 260 with a GMPP 572, GPS speedo read 81 mph, which was impressive, however when he lifted the throttle the boat started chine walking terribly. I am talking out of control on the verge of spinning it out. He has since started backing out of it easier. It did not do this with the 496 in it, ran an honest 65 or so. Has anyone else experienced this behavior with this hull, know any fixes. It does not have external steering and runs a Bravo 1 4 blade 28 pitch. We were turning it around 5100 RPM's.

sounds like he should back out a little softer.
also as stated steering should be beefed up when the motors are beefed up

External steering is a must unless u have a death wish. Full hydrualic!

upon deceleration the boat is falling of the pad with the sudden lose of torque, hense resulting in chine walk. When the boat is under accleration or at speed the boat is "hooked up" to the water.

This problem started to occur on my boat at one time and became worse. The king pins an gimble ring became worn. It did exactly what you said. When on a high speed pass when backing off the throttle quick the boat started to dance around almost out of control. The results were from a high torque engine when lifting the throttle quick the drive kicked back and from play in the gimble it made the drive slop back and forth.

I replaced my gimble and pins and problem solved. You should not have to babie your throttle down at the speeds you speak of the boat should just lay down in the water at any speed.

Full hyd. steering is the best and safest way to go this will slow down the ware on the gimble and pins.

good point his gimbal is probably shot.

Redo the whole gimble assembly and install full hydraulic steering.

It's easy to go fast.

It's expensive to go fast safely.

I have to disagree Brian, its not easy to go fast but its definately expensive to go fast safely!