Well I have been having the same problems and we switched to a tub, and it did nothing to help with heat, it was exactly the same as the glass tank. All it did was make the humidity higher. And, because you can't put a heat lamp on plastic, we have now switched back to the tank. I figured if I needed a lamp and a UTH, I'd rather it be in a glass tank.
This is just so difficult! I'm literally going crazy, buying and returning things because everyone says something different and it never works.
So, our ambint temps are still not at 80, they are at 75, but its better than 70 which is what it was in the tub. let me know what works for you in the end.