you're boarderline burning it up.
this will sound counter-intuitive, but here you go! - your heat input is fine and could stand to be a little hotter. you're just welding too slowly and the average heat input is becoming way too high as the material heats up.
whatd you use on the strut tower bar? get you some ER80S-2 or ER80S-6.
watch where you are scratching your tungsten. You should scratch inside the weld area prefferably closest to the root as you can.
when you want to stop welding, toss your filler (clip the last inch off before using the rod again) and back off your heat input while you slowly pull your arc away until it goes out. you're probably close to getting star & crater cracking.
remember 10 seconds post flow per 100amps.
pretty good first effort