I think it is a better idea to try heavier oil and stiffer springs. Crawling isn't completely based on flex and suspension travel. If the CG (center of gravity) and weight bias are off, no amount of suspension travel or flex will help. In some cases, too much flex can make the truck perform worse since it raises the CG, and makes the car more unstable. Usually, you want a low CG, and front weight bias. To lower the CG, try heavier beadlock wheels, metal portal covers, or axle housings (try to not make it too heavy).