User manual did not state when to perform first oil change, so I assumed 3000 miles. At first oil change lube center said that vehicle was 1 quart low. I didn't think much of it, attributed it to break-in period and so-forth. At second oil change (6000 miles) lube center said that oil did not even show on dip-stick. After draining, they said approx. 3 quarts came out (should be 5 quarts). I contacted Isuzu customer relations and they asked me if I read my user manual. They said that this is absolutely normal for a vehicle to use up to 1 quart of oil every 1000 miles. After hanging up in discust, I called the local dealership. The service guy who answered said and I quote "all new cars use that much oil, it's totally normal". The vehicle displays no signs of leaking or burning oil. What should I do and is this normal?