hi i was having the low hot water problem just today and found this page ,
after tearing apart my delta apart i eventually found the problem was not
in the cartridge at all but a slug of calcium / lime that had built up
at the back end of the "hot" hole that the cartridge fits into "top
right on mine" after some deft work with a drywall screw and some
tweesers i got it out and did a 10 second flush with the cartridge out
"carefull here have someone hold the shower curtain to the wall lest you
end up with a very wet bathroom"