Even with a very high pressure washer you can always select wider tips that spread the water and reduce the force on the truck. And you can keep the tip farther away from the truck, which also reduces the force. I've used mine several times, but I put a 40 degree tip on it and keep it about 10" away from the vehicles. It's a 2700psi washer, and with a 15-20 degree tip it peels paint off wood at 4".
I use a 25 degree tip on a 2700 psi washer. if I have a stubborn bug or dirt spot, I will get it pretty close and haven't had any issues at all. It has even been safe for the plasti dip on my front RAM letters and wheels.