'88 Geo Tracker won't shifft

I have an 88 Geo Tracker with a 5 speed manual transmission. I changed the tranny after my daughter blew the old one. Now I am having great difficulty shifting, Particularly in 1st, 2nd and reverse. Also, the hotter it is outside or the longer I drive, the worse it gets. I suspect part of the problem may be the clutch cable. However, I suspect there is more going on here. Any help?