2003 HD

Have a 2003 chev silverado hd 6000 engine, automatic, 4x4, 4 door and probably every option available for that year. Problem is won't start and I believe is passlock/theft issue. Started and quit within 3 seconds. Went to crank 1 day and nothing except all parking lights on and steady lock/car light on. What I've done to date:
-recharged removed batteries(has 2) used load tester:1 good,1 fair.
-tried the reset 30 minute many times, light will not go out, and every time crank park lights remain on till I disconnect both neg. terminals so I keep recharging them while doing the reset, no luck.
- Certified GM mechanic (friend) changed the ignition switch but not the key cylinder. Checked all fuses inside and under hood- all OK. Took apart outside fuse box and is going to get proper cleaner to clean all the pins and slots.
-Always getting different messages on dic in truck, service 4wheel drive, batt rmt low, batt 2 low,etc.
-Plugged OBD II code reader and cannot communicate with ECM. Checked with his truck and reader is fine.
-Any suggestions and thoughts are most welcome and thanks.