Hi Terry,
The only time tire size will affect the ABS, is if you run different size tires. If all 4 tires are the same size, you are OK. You didn't say what year truck you had, but in most cases 30's will work on stock trucks. I have 31's on my 97XLT and they worked great for me, even before I did a torsion bar lift.
Hope this helps. Dead Link Removed
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Happy Wheelin'
Ray L.
97 XLT 4X4 4.0L SOHC