1998 Chevy Lumina Transmission issue and enige issues

I brought the car back in Feb. The girl I brought it from couldnt remember when she had a tune up done, oil change or anything, so I took it to have it all done, since then on cold starts SOMETIMES it sounds as an airplane is about to take off, you can drive it like that but I will gain speed without my foot being on the gas, and I really have to press hard to get the brakes to work, I replaced the brakes two weeks ago and since then the brakes work fine, but the enige still idels very high. A friend said that it could be the idle meter, but I cant tell because I dont have the thingon the dash to tell how high it idels. So what could be making it do this?
Next question is when I go up hills, I lose power and have to press the gas patel to make it up the hill and for take off from a complete light I have to do it too. Someone told me that it could be the tranismission going out, but I had someone else look at it and they said that it could be something else? So I am at lost with what to do or where to being if you could help that would be wonderful. Thanks