When offroading axle flex is key. In most cases it makes more difference then power, after all what good is 300+hp if you can't plant it to the ground. One day I was driving in my back yard. I saw a hole, it looked just right to fit one tire in. I was hoping to get stuck in the hole, so I could finally use my Hi-Lift jack. Sadly my truck simply powered out of the hole, like it was not even there. I must wait till I get truly stuck till I use my Hi-Lift. Any way I put the truck back in, to study the flex. I then backed out and dug it deeper. I also used ramps to push the flex farther. Here are some of the pic's and what I found.

Impact!.

Best to find this out at home. Here we see the tire hits the finder in max compression. if I add speed to this, then finder damage and or tire damage is possible.

When maxing the suspension, check the drive shafts. Make sure they will not pull out, or be pushed in.

Ground clearance. Solid axle trucks have better articulation then IFS types. This is cause as the tire goes over an obstacle, it picks up the differential. Where an IFS type tends to just lift the tire, leaving the center low. In this pic we see that the cool looking "Go Rhino!" axle truss is reducing ground clearance, just a tad. It looks bad in this pic, but really its barely catching earth.

By removing the spring clamps I get a few extra inches of down travel. Cause I drive this truck, I left the front spring clamps on.

Here is another problem. The steering shaft is ready to pull out. This is under a lot of flex. But if I add speed to this, it could be bad. Glad I found this problem in my yard, and not in the desert.

When flexing, things move. Under the hood we see the radiator moves close to the frame. Any closer and the bottom tank will be pulled off. When the truck sits normal, the bottom tank is about 3" lower from the frame.

Check the shackles when flexing. Look for them bending or any thing not normal.

Some other pic's.