transmission help
 

I have a 91 lx with a t-5 tranny. I need to know how to tell if I just need a clutch or if the synchros are going. I can shift 1-2 no problem, grind into 3 and 4, into 5 fine. there is no sound while the car is stopped. it only does this when I am driving. also I am trying to figure out how to correct my speedo which is out 20Km/h (12mph) at highway speed. as far as I know everything is still stock,