initial thought was low voltage at starter, pulling down to about 9 volts, that’s why I changed the starter. Same result. All connections between bat and starter clean. My thinking is it’s turning a tad slow on start.
This may be worth looking into. 9v at the starter indicates too much of voltage drop. This results insufficient cranking speed which is imperative for cold starting.
Consider doing some 'voltage drop' measurements. (use clip-leads to make connections so you do not have to hold the wires)
*) Meter leads connected to battery minus -and- starter case.
*) Meter leads connected to battery plus -and- large wire on starter
In both cases, connect to battery POST.... not the clamp.
For each of the above 2 tests, take measurement WHILE CRANKING and expect less than 100mv (0.1v)
Any more than than 100mv indicates poor connection between those two points.
My tractor APPEARED to have perfectly fine ground wire... but failed this test. After cutting the ground wire, I found it was mostly green powder inside the insulation. A new wire really improved cranking speed.