You might want to try using a strap that won't run the risk killing you when it lets go, and a pull vehicle with a proper frame mounted pull point. That strap you've got is a TOW strap-designed for pulling a static load. You need SNATCH strap that will stretch a little and give you a tug, snatch straps also do not have those brutally dangerous hooks on the end that snap off and fly into the back of your head. You're lucky no-one was hurt using the wrong strap and pulling from the bumper ball.
Sorry, I don't mean to sound like I'm trying to tell you what to do, but I hate seeing people do things that could be done more safely. There was an incident not far from me a year or two ago where a guy ended up with a tow strap snapping and firing the steel hook right into the back of his head. He lived, but just barely and only because they were at a very busy area and a helicopter was able to get there quickly.