Hey there ;-)
The best thing you could possibly do is to share your car setups with other racers.
Just search for a decent Server that suits you and has people every day. When you frequently show up there you will aquire some helpful contacts rather quick.
I did it the hard way. Before i even thought about racing, my content was to be Testdriver for myself. I changed things on cars for months and tested every single change i made on track.
I still share setups i make frequently even after so many years.
Nothing can replace feedback you get from people that are actually using your setups.
And to stay on topic..., if you want to be real quick and want make use of your skills in serious races you should be able to remove minor flaws that your car has.
I wouldn´t rely on others, especially if you are in a competition with them ;-)
The learning curve is a bit steep, but once you´ve made your first steps into it.., creating setups kind of becomes as much fun as driving itself.
It´s one of the reasons this game will never get old.
In LFS you can use a World Record setup from someone else, join some races and still lose against people that improved that same setup for their own driving style. Just had that 2 days ago. A hand full people using the same WR setup, that had no chance to keep up with me, because I managed to get more out of it.
Those were experienced drivers playing this game for ages. Happens from time to time, that even veterans feel slow like you again
Spectating people to gain track knowledge, a clue about their gearbox and different lines that are effective also kind of is very important if you want to be fast. There are Corners and Chicanes in this game that can cost you 3-4 seconds. Just a simple Chicane (As National last Chicane).
You can be the best driver and have the best car setup. But if you dont know how to approach this chicane "OldMcFart" will steal 3 seconds from you anyways