That is a bit off, but you really need to know exactly how far off you are. If the front is 3" higher than the back, at the axles you may only need to raise 1.5" to 2".
Best way to know exactly how much lift you need at the axles.
First find a level space, and part TV and 5er connected.
Then measure the distance from the top of the bed to the ground at the pin location, then add the desired 6" to that and call this Measurement1.
Now, without moving the 5er, disconnect the TV and move forward for clearance, and level the 5er now measure from the ground to the bottom of the 5er at the pin location, call this Measurement2.
Now time for the math, Measurement1-Measurement2 = the necessary lift needed at the axles for level tow.