Nothing wrong with PPG products other than the clear tends to dry back a little more than I prefer causing more buffing time. R&M Diamont line is great. Price compatable with PPG and the clear is freakin awesome to spray and work with.. But thats just my opinion.
What PPG clearcoat are you using that your getting die back? I been painting professionially for 30+ years and never had Concept clear die back. Omni yes but never Concept.