5.7L (Vortec) Suburban with 3.73:1 (ltd slip) and 2WD. Works every time, but there are some ramps at my lake (one in particular) I'd be way too scared to try (steep and a longish way to the top). I don't think it ever even spins the tires, or rarely and only briefly.
The one I use 99% of the time isn't very steep, and I have to get the back wheels in the water to get the trailer fender wells submerged (I try not to go over the axle seals, if that matters, but can't say I never). I prefer almost floating the boat ON/OFF. I had issue at that ramp early on, scraping the underside on a center roller bracket, if it didn't go back on exactly like it should.
That LeSabre's probably an LT1, no?