stress in the finished project cracking weeks later

I have been firing for many years and have occaisonally had  cracks appearing weeks after completion but am currently having almost constant problems, usually not apparent ... same kiln paragon dtc 100, its old and the elements are regularily sproinging out but appear to all still heat up, mykiln sitter has limited capabilities but seems to work, (limited in that I can only program one step at a time)  any way I am not sure if the problem is my equiptment, my technique or possibly my karma.  I have tried to extend my annealing times, ramp up slower, limit my thickness ( which sucks).  I work with both bullseye and systems 96 ( not at the same time) but have same problem with both.  My projects tend to be large 20" x 2o" multilayered but not solid layers as in many small connecting layers with gaps ( space with no glass) and sometimes include wire, brass or copper  generally.  I read your tutorial on thermal shock and appreciate your repeating message of slow down and all but since the problem seems to be increasing  I am concerned about my equiptment.  how  does one decide its time  to  repair/ replace a kiln -  I am getting frusturated and hoping someone might have some ideas.   thanks! alison