I have a 1999 mustang gt with the following mods would a tune help me?
3.73 gears
bbk x-pipe
flowmaster mufflers
70 mm tb
steeda pullies and t/a
c&l 80mm maf
and plan on getting a c&l plenum soon!
I don't think it would do much for you. With the stuff thats listed you're not really putting a lot of stress on the engine(maybe a 30-40hp increase with those mods). As long as the maf is set for your injectors (I assume it is or your car wouldn't run right) then I wouldn't waste the money for a dyno tune.
I know a tune would give you more power, but wait until after you add the plenum and TB.
My car gained 8 rwhp/10 rwtq. from a dyno tune. Plus, you can make other changes as well. You won't have to run a speedo corrector or MIL eliminators after a tune if you tell them to address those things.
You won't need a TA either because they will bump up your timing and you will have to run 93 octane from then on.