i don't know what people have against simple green. i've been using it for years on very very well-maintained vehicles and i've never had a single problem. show me proof that simple green has screwed up your or anyone else's car/truck and i'll believe it. using words like "horrible" would be associated with rubbing your car down with acetone, not simple green.
when i use it, the simple green is on the car for all of about a minute since i spray, wipe/clean and move to the next spot. it never sits on the clearcoat (or plastic) and immediately after i'm done cleaning i either do a full sealant treatment on the area or a spray treatment if its very minor. but seriously, i wouldn't let any cleaner, regardless of how "gentle" or "safe" it was sit on any surface for very long.
Simple Green is fairly caustic with a ph of 9.5. It is extremely damaging to paint and plastic. It breaks down oils quickly, which is why it makes a great degreaser. Spray a little on your fingers and rub your fingers together. The slippery feeling that it creates is the oils in your skin being broken down.
When it does this to plastic it removes the oils and reduces the UV protection, causing it to breakdown and discolor and eventually become brittle. It does the same to the oils in the waxes and protectants on your paint.
Once you spray a caustic onto your truck, it starts the destructive process. Wiping it off or even hosing it off doesn't stop it. You need to introduce an acid to neutralize the alkaline reaction. Most tap water as well as cleaners are fairly neutral and aren't going to neutralize the reaction.
Trust me. I worked in a chem lab for 10 yrs. You should be far more worried about alkaline solutions than acids. So no matter how short of time you leave on your truck, the damage is being done. Keep the simple green for cleaning the driveway, and get something a lot less caustic for you truck.