Will a transmission out of 1995 s10 blazer fit 2000 blazer?

No, a transmission from a 1995 S10 Blazer will almost certainly not fit a 2000 Blazer. While both are Blazers, the transmissions changed significantly between those model years. The 1995 model would likely be using a much older design. Even if the engine size is the same, bolt patterns, computer interfaces, and other critical components will be incompatible.