For 3 years now we have used the following method to remove bugs, tar, black streaks etc. from our rig, when ever it gets dirty. When we finish a trip or are going to settle in one area for a week or more, we take the truck and trailer through a "truck wash" before we park it!!!
These outfits are used to HDTs coming in with all kinds of crude on them. We caution the workers before they start, to keep the high pressure wands at least 3' away from the decals and windows. We also always have them spray on a wax coating when they are through. Occasionally, we have the engine cleaned also. They get to many places we can't.
We have found this method is very satisfying. It really makes the rig shine and seems to protect the finish. It is also comparitvely quick, about 30 minutes from start to finish. [ It used to take 2 of us about 3 hours to so the same job.] The cost for our rig, [Kenworth semi-tractor with 40' trailer] usually runs $60 - $70.
I am approaching 70 years of age, and value my time, strength and safety above the cost of this service. They scrub the trailer's roof and the top of our truck. [13 feet 2 inches] also.