Hello, I'm TV Tech1 and I'll be working with you to identify and help you resolve your problem.
It sounds like the Goodman tuner isn't as powerful as the TV's tuner and that's why you're having problems only with ITV. I've had that happen on certain brands and models out there, and I generally suggest a different brand to try, or a different /higher model. In your situation since you just purchased the unit, you do have that option available to you.
I also find that mid-priced models work more reliably over the lowest priced models too.
Most manufacturers do sell "entry level, mid priced and full featured" models. I don't know where your unit stands in the Goodman lineup....but it does affect the reception quality on a lot of units. My personal opinion is if you get GOOD ITV reception with other equipment in your home, then the Goodman tuner is a little weak in channel 3 reception. That could simply be a bad RF amp, or bad mixer that's not converting channel 3's signal very well.
I've checked the reviews online, and I kind of expected a balance of good and bad reviews, but it seems overall, a lot of people are having issues with it. Either people really love it, or they hate it, there's no "in between". It may very well be that if you get a good one they work excellent....but if you buy a bad one....it's time to swap it at the store you purchased it at.