I just had my 5.7 liter vortec engine rebuilt. I've got about 9k miles on it and I'm noticing that in 5k miles im adding 2 quarts at 2 separate times. After that when I changed the oil only 2.5 quarts came out. The first oil change was done by the mechanic after 500 miles. The 2nd one i used gtx 5/30, this last time I used valvoline 5/30 synthetic blend. I did read that the oil burning will get better bit it has not. I have 6k more miles till the warranty is up. Should I be burning that much oil?