In the case of my previous 98 gt, the panel behind the headlights was cracked/busted so no amount of adjusting could get them to aim properly. These are such a pain to adjust! I gave up and jammed a twig underneath mine to keep it aimed upwards enough, but it was always a issue.
I had difficulty getting my headlights on my old sixer to adjust correctly. The beams crossed each other and no matter what I did, they just didn't adjust the way they should have. It turned out to my shit aftermarket bulbs. For some reason they were messed up. When I put the old OEM bulbs back in, I could adjust them right to where they needed to be.
I got tired of jacking with the plastic tab adjusters when I installed my aftermarket headlights. I finally got some nuts and lock washers and took off the plastic tab thingies and threw them away.
Every 3 months I cut out a piece of cardboard box, fold it in half and squeeze it under both headlights. I always have to replace them because the cardboard gets soggy when it rains but I've been doing this the past year