1995 buick lesabre automatic i passed a truck and i got on the gas hard floored it. when i started to slow down it quit working. i stopped check fluid which was ok i had no reverse and no forward unless i put it in third gear.when i reach 40mph the trans would quit working but would kick in below 35mph the car has 216280 mi.fluid has been changed on a regular basis

Hello , can you shift the car by not putting it in D , but by you going through the gears? I ask because its going to be one of two things: vacuum mod/shift vacuum mod has failed or you have lost a vac line. It may just be the trans had had enough and needs replaced.
Thank you , Quinn

Well, that's lots of miles on this car, althought you service it regularly, the transmission probably was on the last minutes of its life when you floored it.

The over drive which is 4th gear in the transmission has a solenoid to lock in the overdrive. Have that solenoid checked out