Did you have the Tune swapped before/after the 408 install, or all at the same time?

he did the tune back in january, that made a BIG difference in drivability.the gears really woke it up. that was just last week. they did a great job. they recomended the bushing as well. no more wheel hop. even on cold pavement. cant wait till summer. the launch control may work great then, without blowing the tires off.

so question, does srm still work? and does it mess with the speedo?

yes it still works. i think its off just a touch, but not really noticable.

Speedometer should be dead on with factory diameter tires; as the speed sensors (2) are located on the output stub shafts...they read it there/ so 3.36,3.69,4.08,4.36 shouldn't change speedometer.....not sure about other features.

Or ecu tek can tune for 4.08 gears

Except 370Z's are out by about 10Kmh at 100Kmh. My speedo reads 100Kmh when I'm going about 90Kmh.:wtf2:

That's 10% (6.2mph) either you have put very short tires on your ~Z~ or something else is going on....mine is near perfect with new rear tires (26.8,26.9") but as they wear down,you can get 1 to 1.5mph slower than readings of speedo....only 1-2%.
You may want to have something looked at/as i haven't heard of one being that far off.