yes, this is unfortunately exactly my experience too.
sorry, this was supposed to have quoted Mister T's BBQ's post, but it seems to have disappeared. Here is it:
"This has done nothing to fix the issue with my Pro 575. I tested it yesterday. Grill was set to 225, RTD probe read between 240's and250's with actual temps being in the lower 180's to 190's. Set at 450 it reached just above 350. I've had this grill since march, it took me 18hrs to cook a 9lb brisket and I'm pretty much at the point, I hate my $800 grill, and will be calling about returning it today"