TW5500 hi-hide white is some aggressive stuff, great ink but no fun on the press.
Max slow retarder, not the std but the slow.
Put some slow retarder/distilled water in a spray bottle and rehydrate with that.
Harden those screens. We use Murakami Hardener MS which is reclaimable but at 1k+ I might just sacrifice the mesh and apply their Hardener A+B. Pert near impossible to breakdown a good stencil with the permanent hardener on it. TW 5500 series just plain needs this, it's not a band aid, you're doing everything right with exposure and have an excellent light source.
What bulb are you running out of curiousity? I always like the L1250, oem Olec, worth the coin.
SP-1400 is a little "soft" for some of this work with graphic inks. I like Nova with diazo on thinner stencils.