If it is over the limit of the forklift then dont move it,
i have been driving since 1975, i can do most things, even this can be done, but is not within the capacity of the forklift so should not be moved or try to lift.

Surely the relief pressure on the lift is set higher than it should be ?
I would imagine that your employers don't worry about having to pay out for new forks, mast rollers and steering axles on a regular basis.

Yes. A Osha inspector will soften up their position.

you don't need to complain to OSHA, just keep your hands and feet inside the operators compartment, be sure to -ALWAYS- wear your seat belt, and get the instructions in written form, and signed by -all- the operators, so that everyone is following the same rules.
That way, when the forklift needs a new steering axle and knuckles for the third time, and the mechanic explains it is due to the smashing back on the ground the truck does, every time you tip it back on all four wheels, you are not "at blame".
let see, a 4000 lb counterweight dropping from how many feet?

do the back wheels pick up off the ground when you lift a load?
are u using other employees as additional counterweight?
then id say you should make a call

remember those ratings are for a load with a load center of 24"from the face of the forks and 24" up from the top of the fork blades

you have to look at the data plate and figure out the load center of the tub

you should be trained and have the osha cert this is covered in the course
as of 2000 i believe its illegal to operate a forklift without the cert


say if the load center of the tub the way you lift it is 36"
then the rating for the machine's max load would drop significantly and would be very dangerous