Try a new well-greased cable, have the derailleur adjusted for limit screw, vertical height, and horizontal swivel. Make sure the bottom bracket is adjusted properly. Shift to your big ring only from one of the outer rear cogs. If it still shifts like cr@p, you might need a better derailleur or crankset. Alternatively, one way to get faster is to stop shifting so much and force your legs to get stronger and more supple.