Plastic Tub and UTH Help

[ElderDeku]

Are you saying the actual UTH is not getting over 75F?

or,

That the tub temp is not getting over 75F?

The interior tub temp is not getting over 75F.
I didn't put a thermostat probe on the outside under the UTH because the UTH says to make sure there's no air bubbles and I figured having a piece of metal on a hot surface was a bad idea. Also the Zilla probe is really really big.