You rarely see anyone doing weighted stair climbs anymore. The main reason is because they're so damned hard. I used these when training for the Fire Fighter Combat Challenge (the hardest two minutes in sports) but they're great for all-around metabolic conditioning.
It's very simple. Grab a set of dumbbells and walk up the stairs as fast as you can. When you get to the top, walk back down. Rest as needed and go again. Repeat until your heart explodes out of your chest, your lungs collapse, or your legs give out. Whatever comes first.
It's simple, yes, but easy? Don't kid yourself. After 5-10 minutes you'll be done.
It seems like you've been adding weight to the stack each time you do triceps pushdowns. The veins in your neck stick out like a garden hose as you power through the sticking point, and the cable starts cutting into your neck, just like your idol, Tom Platz. You stop, however, before it cuts through and leaves a bloody mess on the floor.