The transmission in stock form without a change in programming will always shift into the next gear at 6200 regardless of what you do. It will even make the shift from 4th into 5th at 6200 that would be at about 170. I have a 2006 SRT8 300 and when I first got it I could hold it in gear until 6400 when the fuel shutoff occurred and the car would stumble until you manually upshifted. During the winter of 2006 I got a recall notice from Chrysler to have an updated tranny flash at this time the transmission was reprogramed to shift at 6200 and the stumble was eliminated. I understand from various web sites that some of the early 300 SRT8 owners 2005 and 2006 did not have the tranny flash done and are happy with that. I like the tranny flash, the only thing it has done has made it so my 300 shifts out of 4th at 167 instead of holding up to 173!
I had a '05 Magnum RT that I had tuned with a Superchips tuner and I had it set so it would not shift in Austostick until I physically did it myself. I almost over revved it more than a couple of times (hit the rev limiter). Oh, and my revs never get over 5800, and it still upshifts.
DS will not do that for you. A Mopar Performance TCM module will do the trick for you. Do a search for MTCM. I assume you have an RT and I believe they are available for the "later year" RT's now. I believe Chrysler changed something in the programming possibily in '08. The earlier RT's you could change it with a Predator or a Superchips programmer, but not the newer ones.