Don't listen to anything that Radio Shack Tells you, they no nothing.... Something in your setting is not right, This is a great Scanner and should have no problem with trunked systems. Check your Programming, and read the Manual also the wiki section on trunked systems....Read it till you understand it, and then read it again. as you read it check your prrogramming, and see that it corresponds to the mannual settings.
I see that your not a paid member here, and I would HIGHLY advise getting a membership. it's invaluable.
Being able to download from the data base is worth every penny you pay.. Again Good luck ...