Hey guys; so I got a customer with a 2001 built in the door jam is 04/01... OS that was in the ECM was 15063376 and from what we can gather truck has been 100% bone stock... Here's my issue; customer showed up and we tuned it flashed a 02600605 OS which I have in the past on 01's and its been fine... First thing I noticed fuel gauge messed up... Tried a different OS again 03904405 same thing? I've done some reading and according to TIS the first OS that was in it was 9393838 which some guys claimed was the first OS in a duramax... I ran out of time last week but my last option was going to be a OS 01887305 which a couple guys I talked to said would fix the problem... Its really been bugging me customer didn't care but I like to make sure once I am done everything works like when it came in... Thanks for any pointers!