That certainly looks like a GMC front crossmember.
The GMC engine is just a bit longer than the Chevy and many GMC trucks have a similar modification done to retrofit Chevy engines.
Do you have Chevy or GMC front sheet metal on the truck?
The crossmembers can be changed (GMC for Chevy and vice versa) but the front sheet metal mounting changes when you do.
That is a GMC crossmember. That has had a mount welded to it. When I changed out my GMC crossmember to a Chevrolet crossmember, I don't remember having any sheet metal mounting issues.
