I hear if I try to sell my house within 3 years of owning it that there is a 25% tax I would have to pay upon selling, Can anyone tell me if this is accurate.

It's actually 35%. The 3 years only matter if you have sold a previous property within 3 years using the exemption. You must hold a resident visa and it's supposed to be your primary place of residence. I'm sure the link from Tally Ho explains it but that's the short story. Also in Zihuatanejo you have to have been registered with SAT for 6 months minimum. Even though it is a Federal Statute that gives you the tax free status one notary in particular in Zihua enforces that unusual rule that is not necessary in other places.