Please help need some insight on why my 09 DCSB is uneven at all corner

I have a 09 DCSB with only 40k miles bought it from a toyota dealer no accidents and is in great shape but she sits at different heights all around. all measured from the bottom portion of the center of the wheel (easiest reference for me)

Driver Front Passenger Front
21 1/2 inches 22 inches = Higher on Passenger front by 1/2 inch

Driver Rear Passenger Rear
23 1/4 inches 22 1/4 inches = Higher on Driver Rear by 1 inch


This for the most part is a mall crawler and I am going to be installing 2.5 spacer lift to give me that mall crawling edge lol. Looks like she had a TSB done with the leaf springs ( at least the Ubolts and bracket look brand new and the entire under side has been freshly coated). Another thing I noticed the Bed is almost a 1/4 higher on the passenger rear when measured by the window not sure if that helps maybe the bed seated right?

Questions:
Does anyone have any idea why she sits like that?
Is it safe to put a 1 inch block in the rear on the passenger side only to level it out and a top plate on the driver side?

 

Can't comment on why it's off. But if you haven't had experience with spacer lifts before, it'll give you that 70's ford riding on bricks feeling. I promptly removed mine after about 50 miles. Much better ways to lift a truck.