If your shadows "look a little thin" when you push Tri-X to 800, it's because they are. Pushing film means you're intentionally underexposing it and trying to salvage detail in the shadows while propping up the midtones and highlights by overdeveloping a little. You can maybe get a little more shadow detail by using a compensating developer, but not a whole lot. You can try a two-bath developer like Diafine and maybe have more success. Acufine, if it's still made, is another option. Diafine and Acufine are special-purpose developers made for just this sort of thing.
Better yet, throw a couple of rolls of 120 Ilford Delta 3200 in your camera bag. Its nominal speed is about 1000 and will give better shadow detail than pushed Tri-X.