I don't know much about presol but bugs are pretty easy to get off.
The main thing is to get them ASAP when they are fresh and haven't baked on your truck for weeks. Get a gallon of Autoint's Valugard's Omni APC. It is concentrated at 10:1 so you get a lot out of that one gallon. I mix it up in a 1 gallon garden sprayer and start soaking the bugs on the vehicler as well as bird poop when I start to clean the wheels. By the time I start spraying the vehicle with water to wash I've hit the bugs with the stuff three times and they have had awhile to soak so they are soft and come off easily.
For the bugs that stick or leave that thin residue, then Pinnacle Paint Cleaning Lotion will take care of them easily.
