Help with '94 GP SE

I have a 1994 grand prix and for the most part i love the car but have recently had a few problems, anyone with any type of advice or directions to fix these problems would be a godsend to not only me but my checkbook.

Problem 1--- When the engine is warmed up and I am sitting in drive idiling at a stop light type of situation the car will shake very roughly. The RPMs are usually at about 650-700 when this all goes on. When i have the A/C on this doesnt happen as roughly, when it is idiling in park it doesnt happen, when it is driving it doesnt happen, when the engine is cold it doesn't happen. I have a funny feeling it is something to do w/ a vaccum somewhere but i am just your average joe who can change his oil and thats about it, any ideas.

Problem 2--- When i am on the highway and am slowing down but still have my foot on the gas and the tranny tries to kick down it almost always will hesitate and then kick down giving me a nice little "no i dont want to shift type of kick back" is this just normal, the car has 111000 miles on it.
Thanks for your help if you have any to lend.
Again, any help with my problems would be awesome

Sounds to me like there is a vacuum leak somewhere in the engine. Replace your upper and lower intake gaskets and throw some new plugs , wires and ful filter in the car also. That should be the recipe to alleviate your situation. BTW..which motor do you have ?