shower diverter problem

hello everyone. i am new to the forum so bear with me if i am not correct.
my problem is: i'm replacing a three handled shower. i have replaced the hot and cold with no problems. they work great. my problem is with the diverter. i have replaced it with a brand new stem and i cant get the water to go full force to the shower head. the water does completely turn off at the spout. i have tried replacing the old diverter with new washers, the old stem and still have the same problem. no matter how i put the stem back in i can still only get partial water to the shower head. is there a certain way to align the diverter when putting it in??? there are no markings on the valve to indicate "up" or "down"
any help would be greatly appreciated. i would really like to use my shower again. thanx

First, try taking the showerhead off and running the water out of the arm. See what kind of flow you get. If that works, look at the input to the showerhead, it is probably clogged up with bits knocked loose when you removed the old stuff.