2000 silverado ext cab 5.3 many mods, Truck was working fine then i noticed that it would stall at around 5600 rpms WOT so i checked with autotap and it said bank1 sensor 1 was bad, so i got pricing and was going to purchase then i checked again and bank2 sensor2 was bad now. and bank1 was ok. I checked with efilive and the system readiness fails on the catalyst o2's and something else. i reseted the pcm by disconecting the battery and it was back to normal for 2 WOT's then the efilive said no response from interface and it happened again Error was (received checksum is $6A calculated checksum is $DD.
Can anyone Help??

 

Restart efilive and try connecting again. Seems that efilive will choke sometimes not sure what the sequence is that causes it but it does it to me often.
Getting efilive to connect won't solve your truck problems but you should be able to log data and figure it out.