Indy 500 low/high end bog?

I have a 1991 Indy 500 that has been had a major loss in power. i have very little low end power, but upon takeoff i am fine. when i push throttle to the max i can get rpm's up to 6.5k+ easily. but then it starts to bog down again. it is also very quiet compared to my 440 which seems to scream and has more much more power... btw... has 8k miles on it so it could be just steadily loosing power due to wear.