cannot fill water holding tank past 3/4

So traveling with a half or 3/4 tank of water is ok?I had my hand's full going through some rolling mountain passes with 50 gallons in a 70 gallon tank.I installed a pair of anti-friction sway bar's since and went out once with I believe was about 60 gallons and experienced some sway on the freeway,pulled over and cranked up the tension on them. That seemed to stop it but was pondering the rest of the trip if I really needed to top it off.Dumped all the water on the trip back and the ride was fine.I have as much weight forward as I can but the water tank sits above the rear axle and stretches back where when full should put an additional 640 or so lbs.Next trip will stop at scale station to see where my balance is.