lost all gears
 

1994 chevy silverado 4.3L v6
A few weeks ago got a flat tire and my truck went downhill. The vibration of the ground driving on a flat messed something up in my transmission. After that truck rpms will rocket to 3-4s while the speed remain at 25-30mph. As i go through the different shifts from N D [D] 1 2 it only stays in one shift only. Went to a few mechanics and they said it'll be a transmission rebuild or get one from the junk yard. Not sure what the problem is if it's a big transmission problem or small component. Can't even read the codes cause no shop has the proper system to read the older cars anymore. Tried to put a paperclip trick in the obd didn't work. Been driving it like this for about a week watching it hearing it and now every time i press the gas a rattling sound is on and it sounds like it's coming from the transmission. Before all this happened i drove the truck 10 hours to a new city driving it around for about a week everything was working smoothly gears shifted properly truck didn't overheat going 80mph at certain points. Not sure what to do i'm learning about cars but i'll admit im overwhelemd not studying about cars how they work is causing me a lot of problems. Any insight will be appreciated.

take it to a transmission shop. Probably time for a new truck.

getting a new truck isn't an option but i do have the money for a transmission rebuild for about $1400 they're charging me. Going to the transmission shop they told me what it could be but they it was based on a test drive they did, never pulled out the transmission to check. How would you go about this?

I don't recommend rebuilding it. You'll be back in same boat in a few months.

Pulling out the transmission is a big job. At that point the best thing you can do is put a reman in there, but it'll be worth more than your truck.

Sorry just the way it is with 30yo vehicles.