The full load on a incline is not as much of an issue as the half load. The surge in the tank can be a big issue. I use a 500g tank to water cattle in droughts. it is on two RR ties with a hole sawed out, for the tank feet. the tank is ratched down and will slide on a 6% slope and move when you stop. It is often better to haul a full load slowly than a half load. changing gears in a hill is where you will have an issue also.

800gallons of molasses will jerk a 20000# truck around at a light. remember that side slosh is better than fore and aft slosh. A quick turn of the wheel will stop a Fore slosh.

All bets are off if it is a round vertical storage tank on a truck. that's just crazy.... no way to control the flow in them. But that is 20 yrs of tank delivery talking. Seen the accidents and read the reports. Most tank accidents are partial loads that were driver error.