New motor has truck idling at 20 mph in gear.

[jtinpdx]

Hi All,
I've just finished with a full drivetrain overhaul on my truck including a TH350 rebuild with new torque converter and an engine swap to the 350 HO turnkey. The new motor has the Holley 600cfm carb on it. Picture attached.

I'm not sure it's set up properly yet though and would like to hear what you all think.

The motor runs great. Super strong. Starts right up. But I think it idles too high. And when it's cool, it stalls when put into gear. Also, in drive, it idles at about 20 to 25 miles an hour on a flat road. Seems excessive. Feel like I'm wearing out my brakes just driving around in the city.

It was put in by a GMC shop that seem like they know what they're doing. Service manager says that the engine is "cold-blooded". Runs cold. Takes a while to warm up. And doesn't act right until it's fully warmed up.

It's pretty frustrating though to have to let the truck run for 10 minutes before I can even get it out the driveway without stalling.

What do you think?