My 2000 mustang v6 3.8 l started shaking out of no where from startup to every speed its only not to bad when coasting ive changed harmonic balancer motor mounts spark plugs ive brought it to 2 mecaniques that just cant figure it out im gonna change the trans mount this week but do you know what else it could be

you might want to check the torque converter....if it does it at a stand still position the only things turning are the torque converter and the harmonic balancer...My mustang is doing the same thing and i'm almost positive that its the harmonic balancer...but were gonna get under the car take off the torque converter shield and see if something wrong with the fly wheel before we spend any money... that's the good thing about having a father thats a mechanic that's worked on any type of car you name it lol...so yea check the Torque converter if you have already checked the harmonic balancer..Hope this helps! you might want to check the torque converter....if it does it at a stand still position the only things turning are the torque converter and the harmonic balancer...My mustang is doing the same thing and i'm almost positive that its the harmonic balancer...but were gonna get under the car take off the torque converter shield and see if something wrong with the fly wheel before we spend any money... that's the good thing about having a father thats a mechanic that's worked on any type of car you name it lol...so yea check the Torque converter if you have already checked the harmonic balancer..Hope this helps!