I had the same problems you're having with my UTH when I first set it to test out the new enclosure before bringing her home... I was using pretty much the same UTH as you, except a PVC Viv similar to Animal Basics... Here's what I learned from a week of monitoring it: It's crap. It would heat unevenly, patches would be 3-5 degrees hotter than others, it was a pain in the neck to regulate at all... Even after hooking it up to my herpstat later, it was a pain, never stayed constant, and was more trouble than it was worth.
I was lucky and was given some flexwatt along with my BP, it heats evenly (except when I knocked a clip off centre while moving, which was easily fixed) reliably and pairs wonderfully with my herpstat. For awhile I was using both the flex watt and the UTH on the same herpstat, the UTH would heat unevely as all heck, but would at least stay about 5 degrees cooler than the flexwatt to allow a bigger temp gradient...
All in all, I wouldn't recommend them.