I have to second what NT2SHBY said, easy up on the tire dressing a bit. you may be having some of your dressing stuck in the groves and outter tread of the tire, may not be easily visable to the naked eye but once those tires start spinning....well, SLING happens as they say.
I use
Meguiar's tire gel (purple stuff ) applied with a foam applicator and i get very little sling with that product. At time I have layed it on thick (just because I like the very wet look on my tires) and I do get some sling. I do get a lot of sling when I use Megs
hyper dressing applied with a spray bottle...of course hyper dressing is a more liquid product and does fly everywhere when using a spray bottle.
Try this, carry some QD and a terry towel (or MF) in your trunk. when you first take the car out for a spin after your detail then, wherever you stop, just give it a spray and wipe to get rid of the sling. Works for me.