a stall allows the engine to rev up to a specified RPM before the engine locks up solid to the transmission. It's kind of like revving a manual transmission to a specific RPM and then dumping the clutch. The advantage is that you get up to the sweet spot of your cam/engine combination before launch at the strip. Be sure to get a truck convertor if you buy one, they have a stronger clutch set internally. People talk of STR but there is no industry standard definition for what STR is. I believe it's a rating telling how hard the transmission pulls in the rpm range between idle and your stall RPM? 2.4 seems to be what most guys go for. Mine would be about a 1.5 probably since it will hardly move the truck until about 2000 rpm. If you daily drive your truck you sure don't want my convertor. my engine lives between 4000-6200 rpm during acceleration but it does lock the convertor and act normal during cruise, 52+ MPH in OD. It doesn't take long to get there.