new trouble with tank

So, i've had my girl since September of 07. she's growing, eating, pooping, urintaitng and everything else regularly. she is a pleasure of a pet to have.

so on with the problem, i have her on a 20L glass tank ( locking lid, etc ). i changed her substrate and fully cleaned the tank out as i do once a month normally after she sheds ( i spot clean 5 or more times a week ). i've cleaned the tank probably 4-5 times since i've had her and since i got my new thermostat ( a johnson ) i've never had an issue until now. i can not for the life of me get her got side temp above 82.4 . this is not hot enough!

specs :
age : sub adult / juvie
enclosure : glas 20gal long . top has seran wrap, tin foil and duct tape.
UTH : zoomed and a CHE to keep ambient air temps up ( i don't have issues with humidity ).
thermostat : johnson
temps : hot : 82.4 , cool 80.1
humidity : 45-50% ( i havent misted yet today ).
substrate : newspaper ( 5 sheets, one section on cool side one on warm,. they overlap slightly in the middle ) with a thin layer of aspen on top. ( i already removed one layer of news paper thinking it was the problem. the temp raised about 1 degree F and hasnt gone up since then ). i used newspaper successfully before and am unsure of what the problem is.

im using an accurite thermometer and a second thermometer to get the temps in her enclosure on the hot side. the probe is OUTSIDE the tank on the bottom directly on the UTH to get exact readings, the other thermometer is inside the eclosure. they are all digital.

this is the first time i have ever had a problem keeping her enclosure at 88-90F since ive gotten the new thermostat ( ive had that since November ).

the temps in the house do not change and it is normally very warm in the room she is in. i have the termostat running around 100 or more to get the temp up in the cage and it isnt doing anything. i check it frequently.

i'm debating switching her to a tub because of this. but i'd like to see if its just something very simple i'm overlooking.

Hmm, have you lifted that side of the tank enough to get your hand under there and check the UTH to see if it's still working? I once had a UTH, fairly new, quit and die on me all of a sudden.
Also, have you used another measuring device, such as a temp gun, to make sure your thermometer hasn't quit on you?

These are the only two things that come to mind at the moment. Normally temps don't just drop and stay down without reason.

I had my uth just quit on me one day as well. I unplugged everything including the controller it was plugged into and plugged it back in. It works now. If you know the UTH is on for sure I don't know what could be happening.

the UTH is warm, almost hot to the touch so i think its still working. i also have 2 thermometers on that side so i hope they wouldnt both quit on me at the same time ( ones the accurite and the other is just the regular "digital outdoor thermometer"