"Weighted more to the undergraduate experience, U.S. News & World Report ranks the top 100 Tier 1 national universities. On this list are Rice, Texas A&M, UT Austin—and SMU."
Right out of D Magazine:
D Magazine: SMU Goes for the Top - SMU
Now, I don't know if different websites, research programs or organizations have different standards for different tiers, but I DO know that many consider SMU Tier 1.
Maybe when you're talking about research, SMU is not tier 1. I don't know. But ... sources clash because I have seen it listed as a tier 1 university.