Synchronizers shot?!

'89 ford probe GT, 120k miles. Tranny recently replaced with a rebuilt used Tranny, 10k miles on it. Hydrolic cluch master cylinder and slave cylinder replaced(new). Hub bearings replaced. The car is started in neutral, high pitch whinning is heard comming from transaxle and changes pitch with engine speed. When the clutch is disengaged, the whinning dissapates. Shifting into first gear is very hard to impossible, usually have to turn off car and start in first gear with clutch disengaged. Shifting into 2,3,4,5 are all very hard and equally hard it seems while moving. Like I said, the tranny is fairly new although rebuilt, really shouldn't be the synchro's right? All most seems like the clutch isn't disengaging or something like that. The tranny fluid is fine, using ATF right now, what the manual says to use. I installed the tranny myself, and I'm just a backyard mechanic. What are some things that may have gone wrong? What are some sollutions? Someone has suggested worn shifter bushings. I'm not sure what these are or where they are and whether or not that is a common or related problem. Please enlighten me.