Multiple issues with electrical and transmission. How to diagnose?

[AFournier]

(Apologies for the multiple post - my other one was posted in the wrong year)

 

Alright this is a long one so I'm trying to keep it brief in point form in hopes that there's a mechanic out there that can point me in the right direction:

 

2016 Silverado True North Edition - Z71 5.3 crew cab with 6.5' bed - bought new - no accidents or odd events like floods that I can recall.

 

60,000km starter failed

125,000 battery failed and replaced

150,000 second battery failed and replaced (was told had a bad cell)

140,000km Running tail light out - can't figure this one out - bad harness somewhere - possibly due to truck cap installation using "splice" connector when truck was new

150,000 second battery failed and replaced (was told had a bad cell)

150,000km AC control button LED light out on feet+window defog button

155,000km transmission failed and rebuilt by Mr Transmission - a shop that does these weekly

155,000km after transmission rebuild I got multiple codes - had to replace O2 sensor

165,000km trump went in to limp mode and then it went away the next day

170,000km P0420 codes - exhaust definitely smells stronger now so this may be unrelated

175,000km P2101 + P0420 - started up yesterday and super rough idle - "Reduced Engine Power" on dash - turned off, cleared codes and went away. Now the P0420 comes on more frequently as I'm driving on the highway.

 

175,000km transmission has been acting up since rebuild - has been in shop over 45 days in past year - torque converter replaced again - TEKM board replaced multiple times - programming has been altered - solenoids replaced multiple times - shift reset adapt done over 5 times - multiple symptoms persist: shifting erradically "bumping" when slow acceleration at 70km/hr - 90km/hr+ - shifting hard and "lunging forward" at 15km/hr going slowly downhill - and generally shift hard (might be due to "shift kit" they installed as they've told me.

 

Battery tested this morning and reading consistent 14.30-14.5 V after idling for 5 minutes. Is this the only way to test the alternator or is there something else I can test for?

 

Is it possible that I'm just having bad luck and none of this is related?

Edited February 18 by AFournier