heat gun

Hi all. Need your advice. I've bought a house where the previous owner must have had shares in a gloss paint manufacturer as there's about 2 inches of the stuff on every surface, mainly internal door frames. I've tried using a heat gun then paint stripper, but there is still patches of paint...

Image of partially stripped step below. I'm very new to DIY so apologies in advance for any silly questions. I am using a heatgun (350c) and ffp3 cheap mask (£5). I plan on painting over once stripped. The step (for example central section back) has very tricky to strip small parts of paint, ...