need help!! not sure what exactly is wrong...

I just got my moms old blazer and there are a lot more problems with it then i knew. First, there is a annoying rattle noise coming from under the car which i am pretty sure is the catalytic converter. one other thing is the constant rocking of the car...basicly it runs like "poo" from what my friend told me. But the main problem is this, and the reason for this is it almost got me hit by another car the other day. Sometimes when i come to a stop sign or when i first start the car and i push down to accelerate it doesnt do anything for a few seconds then shifts up real hard. And as i was turning going to work one day this happened right in the middle of the turn and i almost got hit...now im not sure if its the trani fluid. I checked the fluid and it was a bit low but i put more in and it still does it. Someone also said that because it was sitting for about 3 months before i got it the fluid might have setteled through the filter and clogged it up. Just though i should get a second opinion before i when and got the filter changed because i was told its a few hundred bucks. Any information would help me out greatly and thank you!!

Have you covered the basics? Change the sparkplugs, replace the air filter, possibly change out the AT fluid and filter.

Consider changeing the fuel filter, sounds like you have trash in it , also does it stall out when you are low on fuel?
Also, if you are gonna do a transmission filter change, its not hard to do. and you can save the money for something else, and invest 12 or 15 bucks in a haynes manual for your vehicle. it will save you alot of money, plus you can learn alot about your vehicle.

Good luck

i have a 86 blazer s-10 4 cyclinder..it dies at a stop but restarts..no check engine lihgt comes on replaced o2/base gasket on carb/fuel filter..need help also replaced plugs and checked cap/rotor