Ok, No way for me to have a 100% answer as it is intermittant but some info that may help
First, I realize you say starter was checked by the shop but,. it will test good evertime when problem not happening. they can ONLy test and confrim good when you have a no crank situation. i trust battery is ok, you tried jumping so,, this leaves one of like 3 things.
ignition switch? trans range sensor? or starter
If you tried neutral when you had the no crank, then this kind of rules out the trans range switch if it no crank in uneutral so, narrows down to ignition switch or starter
my thought? starter, A starter failing can be temp related and work one day and not the next etc
To test starter and igntion switch, one needs to get it to no crank, get under car, get to starter, probe the SMALL wire at the starter while someone tries to crank and holding key in crank position
If power? then switch ok, bad starter, if no power? suspect switch
To me? I am leaning to failingstarter. if they say it tested good when a no crank then yes,, i would back up to igntion switch but,, I am unsrue how they tested starter when problem was not happening so it is inconclusive test. i hope this makes sense
Starter is on back side of engine as shown
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