1996 Blazer not running right

Hi, I'm not real automotively intelligent, so I hope someone can make sense of my description and maybe give me some tips. When I first begin to accelerate, the engine seems to be running high, and it's loud, until I reach 20-30 mph, then it seems to kick down and run fine. My Blazer has 90,000 miles on it, and has run great so far, however this has been happening a lot more just recently. I would appreciate any advice on this, I want to have it checked out if it's something serious, but I'd also like to learn about my vehicle and if I could check some things out myself. Thankyou.

run high?

What does that mean?