I have a 2008 mercury sable. Its an automatic. I was in stop and go traffic this morning on the highway and I went to accelerate and the Rpm shot up as high at they could go and stayed there and the car was making a loud noise and the car would jerk like it was struggling to go. This happened 3 or 4 times. By the time I got to my exit and on regular roads it drove just fine as it did before
Sounds as though the transmission was "slipping" - often this can be traced to problems with the transmission fluid (ATF). Either fluid levels being too low or the fluid being burnt (through having overheated at some point in it's life) - it can be from wear or damage to the torque converter as well but you'd probably be seeing that more consistently.
First things first is to check the level of the fluid - and add some to bring it up to the required level if it's low (running with too little transmission fluid can cause serious and expensive damage to the transmission's mechanics!)
IIRC the Sable should have a dipstick for checking the ATF level in the engine bay - it should be located between the engine block and the airbox (near the front and slightly to the right of center).
To check the level you should have the engine running the pop the hood and unscrew the dipstick, take it off and wipe the end clean with a rag. Then re-insert the dipstick fully and take it out again. There should be two marks on the end of the dipstick labeled "MIN" and "MAX" - if the level is sitting at MIN or below you should probably add more fluid. The car's user manual should have details on what is the correct type of fluid to use and how much to add.
Fluid is added through the same tube the dipstick is normally located in - add fluid slowly in small increments as it can do damage to overfill it and it's a real pain to get it out if you have.
On the other hand if the fluid level is at or near the maximum mark you could be looking at either burnt/degraded fluid or mechanical wear/damage to the transmission and you'd probably be best off taking it to a trusted garage/mechanic familiar with transmission issues.