@Star4900 Have you changed your throttle sensor in your isx (can't remember exact parameter it's under) from automotive to variable speed? It really wakes up the isx. Gives it a lot more power earlier in accelerator pedal position rather than having to have to push it way down to make it move decent.
That is strange a dd13 gives you 1850 and only 1750 from the big brother. The 09 455 I'm in is a gutless wonder with only 7k in the box. I88 in ny and on the mass pike I have to drop a gear on some hills. Heck even some thruway doubles pass me..... My dads little E-7 in his 93 ch will out pull it.