Just the other day going to work I noticed that going into anything after 2nd is tough to get into. The transmission was dissasembled when I bought it, looks good, no metal flakes on the magnet or anything like that. And if I try rev-matching, it just grinds bad into 3rd 4th and 5th. The transmission received GM Synchromesh when installed so it shouldn't be anything with the transmission itself. The pedal kinda feels a lil spongey... Could it be something where I just have to replace the slave cylinder or what?

 

Also, I've tried it at different RPM's so it doesn't just happen at a certain high or low...

 

if its a hydraulic problem(clutch master or slave cylindeR) check to see if your fluid is low, if it is, then look for a leak.

If its not, then its something to do witht he driveline. Maybe synchros or something with the clutch, or even the shifter or possibly even the shift linkage.