I haven't used that brand, but have seen similar difficulty both by applying high-gloss myself and when a contractor used high gloss paint. IF it is decent paint, thinning it should improve flow and leveling. Penetrol is good stuff that I have used to thin semi-gloss to use in a sprayer. Alkyd paint can be thinned by adding up to
10% Penetrol. Flood.com has like product for latex paint called "Floetrol". Check it out, here: