It's most likely the 3rd gear synchros. You can take it to a tranny shop and have it rebuilt, or open up the casing and do it yourself if you know your way around trannies. A used GSR/Si tranny usually goes for about $6-700 give or take. A used 4.40 R tranny is usually around $1200 and has shorter gearing and OEM LSD. A 4.785 R tranny is usually around $1500, and has even shorter gearing and also has OEM LSD. Any B series tranny will work with the longblock. If it's a hydro tranny, it'll bolt right on. If you want to run a cable tranny, you'll need to get the hydro>cable conversion kit that I believe either HCP or HASport makes.