I got a 99' Trail Blazer about a month ago.I was just wondering is it only supposed to go 55-60mph?

So no one knows?

i would say probally 50mph tops,with some add ons like a pipe and clutch kit you might see 60

That is about as fast as it goes.....don't waste the money on all the upgrades..it's not worth

I know it will run faster than 50mph.I ride with a 3004trx all the time, and it tops 60mph, and I can hang with him.I used to couldnt till today.I oiled the chain, and cleaned the air filter.Im thinking aobut getting a FMF pipe, to give a few more horses.

Where are you getting your speeds from? I have never seen a 300 fourtrax got nearly that fast. Assuming you mean the trx300, and not the 300EX. My 2000 Blazer does close to 50 tops. Even with a pipe, you will not see to much more on top. Maybe 1 or 2 mph. You will definitly see more bottom end and some mid range though. It will be very hard, if not impossible, to get 60mph out of the T'Blazer with only bolt on mods.
Don't forget to add a clutch kit with your pipe. It will help the pipe and engine get the extra power to the ground much more efficiently.