Shifters/synchros/trannys

[85MustGT]

I will be needing my transmission to be looked at. If I cruise all is fine otherwise second and third grind real bad. I had the clutch/plate/TO/Flywheel changed last year.
I still have the stock shifter and quadrant. What is it going to cost me to get the synchros fixed? Maybe the shifter fork is bad? What up with the aluminum transmission collar, can you buy a sleeve for it? The engine is stock except for the new Holley carb. It is an 85 GT, I changed the rear end for an 8.8 inch with 3:55s. With the old rear I did not have to shift so much! The most power the tranny will see is if I upgrade the heads and cam in the future.