"Most of the KC-135 fleet have had two engine changes, from J-57 to TF-33 (from retired 707s) to CFM-56."
In actual fact most of the KC-135 fleet have only ever had ONE engine change. 157 Air Guard and Reserve aircraft went through the A-to-E conversion in the 80's, where they utilised the TF-33's and larger tailplanes of retired B-707's, and an entirely seperate programme for USAF KC-135A's which saw 400 or so go from J-57 to CFM-56. I'm unaware of any KC-135's that have gone through all three iterations of available engine (possibly a few of the "queers", you know, "insert another letter in front of the C" jobs!).
The air guard are still happily toiling away with TF-33 engined E models, and as far as I know there are no plans for them to receive CFM-56's.