You can never be too safe under a car, I look back on some stuff we did and it just gives me the chills. This picture in particular-
3 ton jackstands halfway up to do a TTB lift... no frickin way would I be under that truck today. I guess I lived to tell the tale but it SEEMED fine at the time. I remember the truck being a little wobbly.
My buddy and I evaded death one other time when removing a rear axle from a full size Bronco, we had not one but TWO high lift jacks under the rear bumper after the axle was out and they both collapsed at the same time. This all happened while the truck was on a trailer and we were standing behind it holding the jacks... scared the shit out of us both, damn lucky we didn't lose our feet or legs.
Stay safe