The problem:  When riding uphill in sand dunes, 2-wheel drive, the rear end starts to bounce as it looses traction, and I do mean bounce.  Not as bad in 4-wheel drive but still very noticeable.  Everything is still stock when it comes to my suspension and tires.  My question is what is causing this?  Need to adjust my shocks? Need to replace the rear springs (firmer)?  Crappy Tires?  Looking to make upgrades this Winter to my 800 Trail and want to spend my $$ wisely.  Thanks for the help.

My first question is if you have as trail or EX model? The rear shocks are different as in separate rebound & compression adjustments for the EX & a combined adjustment for the Trail model.

You could always pretend you are Steve McQueen, @ 1:02...

https://www.youtube.com/watch?v=_f1oneqYefc

Actually Mine would do the same just before stall-out on a steep soft sand hill in 2WD, lots of suspension hop. Haven't done it again with hew tires and shocks so I can't comment.

2017 ZForce EPS Trail.
Yea that is what I figured from all the various threads on this forum.  It never really quit, but when it would loose traction it would bounce all the way to the top.  Looks like new tires, new springs for the rears and relocking my secondary will be winter time fun for me.  Thanks.

[2015 Z Force 800 53/Trail EPS]

Go a couple clicks tighter (Slower) on the rebound should help for now. The bouncing is basiclt a wheel hop..the accusation and release of traction and the shock allowing the reaction. The stock tires are sh*t too. Overcome it with a different pattern and reclocking so the torque level is high enough that acquiring traction doesn't slow the drive train....or rather won't allow for the intermittent hook-up.

Thanks NMK!