Usually if its a modulator/vacuum hose problem.it'll go into second gear ok,but not third,it'll take shifting it manually or winding it up to 40-50 mph in second gear before it'll upshift into third in "drive" by itself..then once its in third,it'll feel like you shifted to neutral when you back off the throttle,or "coast"..
If all you have is first and reverse,its probably the nylon gear on the govenor,which is located on the drivers side of the rear of the tranny,near the tailshaft--the cover usually either just pries off ,it might have a wire bail like a master cylinder on it you must move to the side to allow the tin cover to be pried off gently--you can pull the govenor out easily by hand,and then see if the nylon gear is chewed up..its pretty simple to replace,just drive the roll pin out and put a new gear on and put the pin back in..I'm sure there is other threads here on doing it!..
