This might be unpopular opinion, but I'm not a fan of plates which echo what's already on the car.
In this case, people who care already know it's a GMT400 and you can buy nice fender badges for the engine's displacement if you wish. Sadly, the car-ignorant crowd doesn't care and so to the vast majority of people out there, your license plate won't make any sense to them. You can say, "F that & them, it's for me!" But you know better, it's a vanity plate and it's there to display your pride, so it's really for everyone else. My vote is something which goes with the vibe of the vehicle or your attitude while driving it. Years ago my ex wife and I had a clapped out (physically, not mechanically) 1990 F-150. We got a plate that said, "KLUNKR" as that's what we knew everyone else was thinking. Loved that plate, and so did lots of folks who got lots of laughs out of it.