Should I buy a new muffler and car radio for my Honda 96 odyssey?

My car is more of a hand me down its got a new battery and a new ignition the engine runs fine but it's kinda slow I know it's suppose to be slow but it seems like I'm going 10 under the speed limit for some reason also the car is really really loud when I drive but it's quiet when I slow down how do I fix this? Also I was thinking of getting a new radio should I get one also? I just want to get another year or 2 out of it before I buy a new car because this is my very first car

Forget about a car stereo, get the muffler and a tuneup, having a bad exhaust system can seriously affect performance and mileage and if the car is that neglected mechanically you probably need a full tuneup, oil change and to get the brakes inspected as well so its safe and runs good enough that is won't break down and leave you stranded