The one thing no one has said yet, is what air pressure you are using?
I have used Tru-Color Paint lately and also find that I have to experiment with different portions of thinner to paint. Then I have to adjust the air pressure. With Floquil and Scale Coat, I would paint between 22 to 35 PSI, depending on my needle size and what I was painting. With TCP, I almost always had to be 35 to 40 PSI.
I would be interested it knowing what others say about PSI and TCP.
RAY