Try putting two hides in, one at each end. Make sure the hides are small enough, particularly for that 120g one.
How are you measuring the temps? Temp gun? Analog or digital gauges?
Are you measuring each tub? Or just one tub and assuming they are all the same? I have the same rack and there are times I see some pretty large variations in temps from one tub to the next.
Have you done just FT feeding attempts? Or live?