Transmission Problems

i have a 1990 cutlass supreme and i think the transmission is acting up.
it shakes and vibrates into gears and idles a little rough. i heard of something on the back of the transmission that can be unplugged some kind of solenoid that stops some problems, any ideas?

That only corrects stalling when hot and coming to a stop, your description is too vague to suggest anything.

Car starts up fine, after i drive it and hit 40 miles an hour it starts shuddering badly, then finally shifts into gear. this all started happening at once i was driving and thought i blew a tire on the highway when i was slowing down. the whole car started vibrating so i pulled over when i noticed a massive oil leak coming from the oil pump drive o -ring, i had that replaced and the car still idles rough and sometimes the rpms just drop to 0 and the car almost dies, with the ac on it sounds like im driving a tractor and runs bad, it also uses alot more gas than it used to before i heard that vibrating noise on the highway. i thouhgt maybe i blew a head gasket cause of the oil leak but the oil level never got that low. i have no idea what the noise is but its loud and it vibrates the whole car.