yeah, try the synchromesh, but dont get some knock off brand.. the gm stuff is kind of pricey, but if it works you will be glad you got it.
but, if it doesnt work, then you'll be one of the majority that have a 3rd gear grind.
and its not cheap to fix. just remember that if you have to do an actual replacement (it may be cheaper to just get a used trans) of the syncros that you replace the actual 3rd gear assembly too. i did it once in a teg i had, replaced every thing around the gear but not the gear itself and it was grinding again a week later. found out after that i should have replaced the gear too. sucks.