1980 chevy k20 wont shift just bought

Hello there,

i recently bought a 1980 chevy k20. i drove it home from about 25 miles away and it drove just fine. but the speedo didnt work and it didnt have a tach. the other night i installed a tach and just ran both seperate wires to reactivate the speedo, but i havent ran the truck yet. i took it out the other nigt after i installed the tach and it wont shift from 1st gear. the tranny has 3 gears and to be honest i dont know much about the truck, its my first work truck. i just added about 3 quarts of tranny fluid and just changed my oil and filter. when i put the truck into gear it shakes the truck very hard, its an automatic, so when i put it into drive. and then when i put it into reverse it knocks even harder. it is also starting to rev very high 1000-1500 rpms when i start it. it jsut sounds abnormally loud. basically the truck wont shift from first gear but it was shifting perfectly fine just the other day when i drove it home. can anyone help me please!?!? thank you!!  

i found what the problem was. i knocked the vacuum hose off behind the carb when i was messing with the distributor. it was a very easy fix and it took one second to find the problem. thank you