Even on otherwise stock engines, I've not heard anyone complain about the M1 intakes, and with more than enough torque to blow the tires off in smoke...there was no way to know for sure if there was any loss in low end.

Now, that is with the R/T crowd who does not tow with their trucks, so the results could very well be opposite in a full size truck that tows a significant amount of weight.

You can add an M1 without retuning the engine and it will run ok, but you can run SCT even on a bone stock engine and pick up power and mileage. With a stock engine or nearly stock, you can run "canned" tunes and not have to worry about custom tuning from running different heads, cams, strokers, etc.