Gary they are Speed limited not RPM limited. Speed limiter is 108mph, but I think the puny tires on the 4. 10-geared duallys will be redline limited (at what speed I'm not sure). .
Evidently MMeier's box can raise the limiter, because otherwise you can throw all the HP at it you want, you're probably not going to break 110mph. I experienced this on my 2001 HO. . . it totally topped out at 118mph when bone stock, and after the vA box and DD2s it topped out at. . . 118mphm but the fuel cutoff was very pronounced after bombing.
Vaughn