Cat removal, tire changes

[sluggerjoe]

Just got a new '05 CC dmax/alli today. I've been browsing the site for some time but have not seen this topic covered.
On the Dodge site they have been gaining about 1 mpg or better by removing the catalytic converter. Has anyone tried this with the Dmax? Also, can a guy put higher profile tires on without hurting the mileage? Maybe 285's? How do you change the speedo to compensate?

thanks

[More Power]

It's important, indeed essential that you reprogram for the larger tire size. This'll make 1-3 mpg difference in either real or perceived fuel economy. I've been hearing that some dealers are offering to reprogram the LLY for larger tires, but a dealer reprogram didn't work for the LB7. In those case, an aftermarket programmer (http://www.thedieselpage.com/reviews/programmers.htm) was/is the best choice to correct the speedo and powertrain programming.

As far as removing the cat, some have experienced EGR codes when removing a good share of the exhaust backpressure. More reading here in the forum could help.

MP

[LyndaLFromTexas]

I have slightly larger tires on my 2002 Duramax/Allison CrewCab 1 ton 4x4 (235 16s).
MorePower says "it's important, indeed essential that you reprogram for the larger tire size. This'll make 1-3 mpg difference in either real or perceived fuel economy." Can you explain why this is. I understand the "perceived" part--since speedometer is off, mileage computations would be off, but is there a "real" difference in mileage that one of the aftermarket programmers will help, leaving everything else stock but whatever adjustment needs to be made for larger tires?) I know the dealership can't reprogram--we checked. My question is, will one of these aftermarket programmers void my warranty like a performance chip will? Or, has it been determined that you can REALLY return to stock programming, after use of an aftermarket programmer, without the dealership being any the wiser? (I've seen other posts about "evidence" being left behind in a "secret" place, but I'm not sure whether that was referring to chips or the performance/tuning flash programmers.) As I've been discussing in another post, I've experienced BOTH the transmission drain-back where reverse disappears (transmission was ultimately removed to replace a spring), and the injector problem (all injectors were replaced under warranty), so I'm a little leary about adding ANYTHING that will give the dealership an excuse to void warranty for future problems. (Yes, I know that a larger tire size can theoretically void warranty, but I think the dealership would have pretty hard time making that stick for engine/transmission problems, right?) Any enlightenment you can offer would be very appreciated. And, while you're at it, I'd appreciate everyone's realtime experience with these reprogrammers on a truck similar to mine (the LB7 turbo).