Put lower gears in your diffs!!! This will give more hp and tourqe at the wheels (which is where it counts!). From my personal experiences with both 2.9ltr and 4.0ltr (same block-bored out,bigger heads/intake) the 2.9ltr is tougher and more reliable. I couldn't kill my 2.9ltr. I Had it in a 2wd, then I put it in a 4x4 with 33x12.5 boggers then 35x12.5 mt's all with stock 3.73 gears. This was over about 4 years. Since doing a 4.0ltr swap about 4 years ago (and regearing my diffs 2 years ago-4.56 gears) I'm on my 3rd 4.0ltr! The 2.9ltr loves high rpm's (me too) but the 4.0ltr has roughly 70 ft/lbs. more tourqe. I regret not regearing my diffs before I did a 4.0ltr swap. Look at what size tires the Toyota 22R spins and what they climb with the proper gearing.