How much difference in cooling does the turbo back make over the cat back? What is the highest temp the egt should reach? Is an intake a must or will the stock work? Please forgive my questions...I had a tundra before the dodge.

I have an 06 cummins with no modifications to the intake or exhaust. Im thinking of getting a egt gauge and then the u7131. My plan(good or bad im not sure) is to check the stock egt's before adding a mile tune. If the egt's get too high with a tune will adding an aftermarket MUFFLER...not whole ...