Need Help Asap - Trans Problem

Okay, I've been having alot of problems with my 99 2dr coupe grand am lately. I believe it is mostly because of the way i drive it, so lately and for now on i have been babying it like hell, going 55 in 65s, and generally 5 mph under the speed limit, normally i try not going over 55 mph because it begins shaking. It doesnt shake alot, but the steering wheel shakes, and the front dash, which i believe is because of the engine. But this isn't my problem. Basically what is happening is every time i go from reverse to drive, or from park to drive and accelorate it seems the tranny doesnt catch and it will rev up to about 6 grand before it finally does, but what i found out is that when i just barely hold the pedel down reving at around 1k rpms IN DRIVE after about 30 seconds to a minute it will finally catch and begin to accelortate. Also, when i try accelorating quickly, not very fast, just a couple mphs faster than most cars my entire engine bay, steeringwheel and front end begins shaking violently. I am kinda stumped on this, i havnt taken it into a shop because i dont have the money to get it completely check out, any one have any ideas?
Also when i am just normally driving around it hesitates to go from 1st to 2nd, 2nd to 3rd, and so on. I think i could be my transmission, but i've seen alot of people mentioning spark plugs being the cause of transmission problems and thought that mabie my 6 cylinder is only working on 5 thus creating extreme knock, or it may be my catalatic converter, if u have experienced anything like this or similiar plz tell me how you fixed it and what your symptoms were so i can attemt to diagnose my own care. Sorry for such a long post just trying to give as much detail as possible, if any of you need to know any more info about it let me know. It is an automatic transmission also. im really trying to figure out whats wrong with it as soon as possible, and i cant really afford to take it in to get it diagnosed right now cuz im saving to get it fixed. Also if any one knows a site or company that carries aftermarket grand am auto transmissions i would greatly appreciate it!

It sounds as if your transmission is slipping. Usually changine the transmission fluid and filter every 2 years is a good idea. Try it. I find it fixes problems like yours about 60% of the time.
The shaking is from something unbalanced, likely tires, but it could also be a bad brake rotor or bad CV joint.
Also, one of the tires could be out-of-round.

could also be some problems with the torque converter engaging properly. might pay to have that checked while youre at it. the vibrations sound like tyre problems.

so the tire problems or unbalancedness which may be the cause of my problems from powersliding around turns or doing 180's on roads? cuz i through and slide my car around alot even in my school parking lot when im bored. Any tips on fixing this so that i can afford to throw my car around and powerslide around turns w/ out unbalancing/damaging the suspention or what ever is now unbalanced?

I ageree. New tires. And a tranny fluid and filter change ASAP. If the filter is clogged you are eating your tranny until it builds presure. Good Luck.