It's better to establish your own thread so that old fools like me don't confuse yiu6r issue with original poster's.
Did you check cables and connections at starter solenoid atop starter too?
Sone possible causes of Starter Motor Cranks Slowly:
Loose or corroded battery cable connections.
Loose or corroded starter motor connections.
Malfunctioning starter motor. Perform starter load test; pull starter and have it tested at suitable shop that has capability to test, including the;
" Voltage Drop Tests; If the starter cranks slowly and the battery is satisfactory, there may be a malfunction of the starter or in the cranking circuit wiring. To determine if the problem is in the wiring, a voltage drop test must be performed on the following:
motor feed circuit
motor ground circuit
These tests are performed to determine if there is excessive resistance in the starter motor circuit. Always make the volt-ohmmeter connections at the component terminal rather than at the cable wiring end connector. Making a connection at the wiring end connector could result in false readings because the meter will not pick up a high resistance between the wiring connector and the component."
A battery cable problem can produce symptoms similar to a dead battery, bad solenoid, or weak starting motor. If the cables do not allow enough current flow, the starter will turn slowly or not at all.
Connect positive (+) lead of Rotunda 73 Digital Multimeter 105-R0051 or equivalent to battery positive (+) post. Connect negative (-) lead to starter solenoid B terminal. note that this the solenoid mounted atop starter.
To locate excessive voltage drop in cable, move multimeter negative (-) lead toward battery and check each mechanical connection point. When high reading disappears, last mechanical connection point that was checked is the problem." by Ford