Elevated ALT after drinking, "resolved"??

Here is my story…
30 year old male, very healthy (6’2” 175lbs) recently separated from the Marines in 2010.  Had mildly elevated ALT (78 on a scale of 6-33) and AST (47 on a scale of 0-40) in July 2010.  Levels dropped to normal after two weeks, serial testing through Kaiser Permanente indicated that ALT would raise (~50’s on scale of 0-50) after drinking moderately on weekend.

The backstory…moderate drinking in college through 2002.  Joined the Marines in 2002 and drank moderately (10-12 drinks on Friday and Saturday) about every other weekend for about half the year.  Through deployments/training I’ve had numerous 6-7 month periods of ZERO alcohol intake.  In July 2010 I left the Marines and went on a two week trip to Key West.  Drank every day, never really got drunk, just enjoyed the trip and the water.  Got a routine blood check with the Veterans Affairs hospital and they found my ALT /AST to be elevated (ALT 78, AST 47).  I followed up with Kaiser Permanente 12 days later and my levels were “normal” at ATL 32 (scale 0-50) and AST 35 (scale 9-53).  Since then monthly serial testing has shown that if I drink on the weekend before I have the test, ALT only is elevated.  If I wait 2 weeks, all seems to be good (normal value).  I have had Ultrasound (normal), all other liver blood checks were normal, chemistry panel was normal, thyroid normal, cholesterol was 167 (HDL of 72, LDL 82, Tri 63), blood count CBC differential all normal, GGT was 17 (scale 11-52), Hepatitis A/B/C all good (tested 3 times).  Kaiser wrote me off as being healthy and the condition “resolved”.  A follow up with the Veterans Affairs hospital last week had my ALT at 47 (scale of 6-33).  Now I am going in for a CT scan ( I had one in 2009 and it was normal).  

I looked over my medical history and noticed one liver enzyme check in 2009 after a deployment (no drinking) but moderate supplement use and it was ALT of 39 (upper limit 40).  Just prior to getting out of the Marines I was deployed to Afghanistan and was taking Percocet, Ultram, and 800 mg motrin for back issues.  My question is this, have I developed some kind of sensitivity to alcohol…has anyone experience a situation like this?  Have I damaged my liver from the pain meds and it need some time to recover? It would be nice to have  a few beers a couple of times a month now that I am a free man, but I don’t want to die from it.  Also, why are the VA lab scales so much lower than Kaisers?  Thanks, God bless.