Intermittent Starting Issues - Lots of diagnostic

Hello All,
I consider myself capable when it comes to auto mechanics but have come across an issue that has completely stumped me. I have a 2003 Nissan Frontier V6 (non-supercharged) (136k miles) that has bizarre starting issues. The symptoms involve random occurrences where I will only get a solenoid click but no actual ignition. If I keep turning the key to the start position it will randomly start. It may be two clicks or twenty. Below is a list of diagnostic and parts changed/tested:

1. Started out thinking it was the starter. Replaced the original starter with a starter from the Nissan Dealer. The issue corrected itself for about a week then reappeared.
2. I jumpered the clutch position switch and it started immediately. I went to the Nissan dealership and got a new switch which fixed the problem for a couple of days. Swapping the old clutch position switch back in made no difference. Sometimes it would start, sometimes not.
3. I tested the resistance on the ignition relay and it was okay but jumpered it anyway (Position 3 & 5 I believe) and it started just fine. I bought a new ignition relay from the dealership but after a couple of days the issue came back.
4. I tested the battery (which was only 1 year old). It tested fine but to be sure I tried to start the truck with a backup battery car start. Truck wouldn’t start on normal battery or with backup.
5. I pulled apart the dash and column to get to the ignition wiring running from the key ignition to the main wiring. It was challenging to tell but it appeared as though I wasn’t getting conductivity in the correct wiring when turning the ignition to start. At this point I replaced the ignition wiring with a dealer replacement. Didn’t fix the issue. Still intermittent starting.
6. I then checked the positive battery cable going directly from the battery to the starter (which also included another wire with two female ends, one going to the main relay box). I was getting around 13 volts on start if I remember correctly. I replaced this cable with one from the dealer ($150) and Hooray the problem disappeared for 6+ months.

Now after the 6 months the same symptoms are back. The only things that I can think of that it could be is the ground wire (which I thoroughly cleaned), a possible short somewhere (shoot me now), or a bad key ignition switch. My question is why did the symptoms disappear for 6 months.

Please help. I love this truck and don’t want to get rid of it but need a reliable vehicle. Thank you for taking the time to read this long post.