all 6 lug truck patterns from GM are the same. i got 17x7.5 wheels off of a 2004 z71 (the flat 5 spoke design) on my 1997 2 door. they look and fit great!
Actually, that is not entirely true. While the 6 lug patterns are the same, the offset is different on older models. Not sure what the cutoff year for Tahoe's/K5 Blazer's is (I think it's 1991 and later), but for GM pickups, all pre 1988 models use a low or zero offset wheel. Everything after that uses a high offset wheel, like on fwd cars. If you try to use low or zero offset wheels on a post 1987 pickup, then the tires will extend outside the wheel wells. I have seen some people run these, but I think it looks weird. Not to mention that in some states it is illegal for the tires to stick out of the wheel wells. But you are correct for everything after that being the same.