First off, a short description of my setup.
I have this rack:


and of course, a Ranco to control the temps:


I recently had horrible temp spikes in my rack, spoke to Rich at Reptile Basics (great guy, btw!) who was
very generous and sent me a replacement kit for the heat tape.
My husband and I installed the new tape, and got everything
up and running. Or so I thought. For some reason, I can't get my temps high enough in the rack!
The Ranco's probe is taped directly on the flexwatt, between the flexwatt and the tub.
I swear, I followed the directions to set up the Ranco to the temps I thought would work, but I can't get
my temps up to where I need them! (all temps measured with Accurite)
As they are right now, 79-82 on the cold side, 85-89 on the 'hot' side. The Ranco is currently set to Fahrenheit,
temp set at 100,
differential set at 2 (I'm assuming 2 degrees from the 'temp'??)
and of course, it's set to H1 (heating.)

Can someone please help me figure out what I'm not doing right?
I am afraid if I turn the temp up anymore that I'll burn through the tubs, and I only have two tubs left!
(The old t-stat or flexwatt had issues, not sure which, but two tubs got burnt up. Hence, the new tape and new t-stat)
Please help!