Loss of power in a 1999 Chevy Blazer 4.3?

hi guys! I just bought a 1999 Blazer 4.3 and for some reason it has a hard time picking up speed from a dead stop! The transmission is not slipping and the cat converter is not clogged up! It does have high miles, 177,000 to be exact! But I had ford trucks with more miles that more power! Is the engine just tired or it it just geared slow? The tires on it are 235-75-15 but I can't see that would make any difference, would it? The engine sitting and running sounds like a brand new one and it has all kinds of power once you get started out going down the road! The only thing I can come up with is just too many hard miles on it! What do you guys think? Thanks guys!

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