You didn't say what year your truck is but I'll have to assume it's either a 94-up or you have previously got 94-up bumper brackets (the middle two, not the outers) installed, for the gap to be like you're describing.
There's no difference in W/T / Silverado / etc. brackets, trim level doesn't make any difference here. It's strictly 88-93 and 94-up. The outer brackets are the same across all years.
A couple good pics and more info would help (what year is your truck for example) - a lot of these parts will mix and match to varying degrees and will kind of "fit" but not correctly, as you've found. Pics showing what all parts you're using - grille, filler strip, corner fillers, etc. help us understand how to help.
Richard