Located at 501 Texas Avenue South, this Diamond Shamrock existed from 1989 to around 1998 when it was closed in the process of the Texas Avenue widening. The convenience store probably wasn't even a full brand, not even Diamond Shamrock's "Corner Store" (which existed as far back as 1990, but I don't believe for any of the local locations until they were converted to Valero). Afterwards, it was absorbed by the U-Haul dealership (formerly Texas Avenue Moving Center) located at 519 Texas.
Diamond Shamrock had previously been a Sigmor Shamrock store (a predecessor company to Diamond Shamrock, though it might have converted to Diamond Shamrock briefly before being rebuilt, as at least one Sigmor store saw a conversion), as was a few others. The U-Haul dealership appears to have originally been on the site of a Philips 66, and records indicate they used a building leftover to do operations, but after Diamond Shamrock died, they moved to that building and removed the old one for more parking.
The style of Diamond Shamrock (black, multiple colors) had to have been more common but no pictures exist of that style on GasSigns.org.