We are flying into LAX tomorrow from Canada en route to Hawaii. We will clear US customs in Vancouver. We are flying AA with our first flight operated by Alaska. I understand we have to change terminals for our onward flight. We only have a 1.5 hour layover. As we will be in transit and already have cleared security and US customs in Canada, I am hoping we do not have to go thru security again at LAX. Our bags will be checked straight through to Hawaii. This is an AA ticket and a legal connection. I know that LAX can be difficult to navigate and I am concerned about long line ups and transferring from terminal 4 to terminal 6. Should I be concerned?

Sorry, you can "hope" all you want but unfortunately there's no "secure passageway between Terminal 4 and 6 so you will still have to go through TSA security again when you re-enter Terminal 6. It's not that far between terminals - probably a 10 to 12 minute walk (or you can take a shuttle bus - they run every 12 to 15 minutes ) - 1.5 hours should be fine, assuming your in bound flight arrives at or close to schedule.

You're going T6 to T4, not the other way. Walk, don't take shuttle as that would have to circle around and takes longer than walking.