2002 5.3L gas c1500 Dual alternator Dual Battery Questions

[mylittlepwnies]

2002 Sierra 1500 SLT 5.3L Gasoline RWD 

I added the AUX battery tray last year and bought a new start battery, moved existing starter battery to AUX tray ( yes, two new batteries is better im aware). Stock wiring for first battery and alternator, added 4ga CCA to positive terminal to 150A circuit breaker(fuse) to a cheaper $80 "smart" dual battery isolator terminal 1 (it has two terminals). aux battery pos 4ga CCA from terminal to 150A breaker to isolator terminal 2. AUX pos terminal 4ga CCA from terminal to 150A breaker to 4ch amp for speakers.
this set up worked great until OCT 23 when i murdered bambi with my frontend and my alternator bracket bent, once i was up and running i was at 14.9-15.6V. from oct 23 to Aug 24 went through two batteries as they kept leaking. replaced alternator. same voltage. decided to replace bracket, bought dual bracket. and a 230A 2nd alternator.  and a 4 pin gen-L connector pigtail with middle two wires. wired L to L I/F to I/F(it has two lines, I and F under it) in parallel. wired alternator output to Starter Pos terminal with 4ga CCA.
this set up worked for weeks, until one night in the middle of nowhere my battery light came on and i was at 11.6 volts I unplugged OEM Alternator and OEM connector and 14.3V came drove home. Tested starter battery, replaced because it read 241 CCA instead of 600... So i bought two CCA600 $100 batteries from auto zone. but every time i plug back in the OEM alternator, i get battery voltage. today i tested starter battery, 194CCA Aux battery at 561 CCA.

What did i do wrong? what can i do better? What better isolator can i get that wont break my bank in the winter slow months of work? What is better way to Wire this? Should I only have L connected to the second alternator?

Ill take all the advise i can get, i have a 12000W split phase  inverter that I want to run in the truck bed this spring summer for work. my plan was to run two 0ga CCA to the truck bed and two more batteries on a cheap manual marine isolator and upgrade the oem alternator to 300A+. but in need to get this set up working first.