Roush Technical Question for speed recal

buying my new gears any day now and had a question. in regards to the speedo being off after installing the gears, i spoke with a friend of mine who said that all i need to do is buy the speed cal ($89) device from dallas mustang and install it to fix any problems i may have. is is that simple? i thought it's been discussed here before and someone said i needed to reflash the entire saleen chip for that. which is true? will the speed cal interfere with the saleen cpu? it's a hell of a lot cheaper to buy and install the speed cal than have my cpu reflashed.

for the record, i've got a five speed. my next question is if i get saleen to reflash the chip for gears and tires, what happens when i go to the dyno and get a tune done? to do a complete tune for the car on the dyno are they going to have to reflash the chip? if so, than i need to wait and put the gears on just prior to getting the tune done so i don't get the chip reflashed twice. can someone let me know? i'll let T&J just reflash the chip for the tune and gears at once unless these aren't related.