I will share my strategy with you my friend.
Put as many Qualifying laps in until you think you've hit your peak, basically you want your best lap to be within a 10th of your optimal, that'll be as good as you get without making major adjustments. Then write down all your best section times once you exit and go to the session results page, so basically take note of what your optimal time was section by section. Chances are your optimal is still a second or two or more slower than anyone in the top 10.
You can watch replays of the top 10 leaders right in the game, pick one. I like to change the view to bumper which I use to race anyway, also switch the setting so it "Displays all race info".
Make note of what gear they are going through turns in, where the starts braking/accelrating, watch their brake and acceleration pressure etc, this is how I learnt trail braking. When they cross the line pause it and switch to the lap breakdown or lap chart or whatever they call it, then you can see their section times. Compare each section with your own. Some you might be faster than them, some might be pretty close to the same which is nice for your confidence, sometimes you'll be just a few 10ths slower in every section, sometimes you will just have one really bad section. Either way you get a really good idea of exactly where your slow.
Then just keep watching the replay over and over until you can identify your issue. It doesn't help to just watch the section you're slow in because usually they carry speed from one section into the next. I think the most important turns are those just before and just after a straight. I find my best improvents come when I take the final turn before a straight as perfectly as I can which will allow you to go as fast as possible through the straight(as long as it's a shorter straight and not a top speed straight) then take that speed through T1 and set the pace for the rest of the lap.
I'm probably no faster than you, I got 1:40.03x on race b this week, so this strategy won't get you into the top 10 but it should help you get over the hump and probably shave at least a few 10ths.
Sorry if TLDR