intermittent starting issues

[OKGMC4]

Been starting the engine fine for months. Then it starts with random clicking. You can turn the key and hear the starter try... it clicks and kicks out the bendix and tries but can't quite turn the engine over. Does it 1 in 10 starts, then 1 in 5 then all clicks and no good. Swapped in a different battery with more cranking amps and no change. Installed a brand new starter and it starts 10 times fine then clicking. When it starts this you can hook up jumper cables and it fires right off with no hesitation. Tried checking ground by putting a jumper cable from the negative battery cable straight to frame and more clicking. Brand new positive battery cable and it clicked twice, but then started 20 times in a row. Is it possible I have a bad ignition switch and it's randomly not letting full voltage to the solonoid? What have I missed?