Verified answer

There's no such vehicle as a 1998 Silverado SS. The truck in question is a custom job. The Silverado SS was produced in 1990-1993, and didn't return until the next generation truck for the 2003 SS. If the only changes to a stock 5.7 are the CAI and exhaust, there are maybe 20 hp gains at best. That would be 255 stock, bring that to 275, and then go back down to maybe 265, accounting for it being an old engine.

there was no SS that year.

Somebody threw some cheap SS emblems on it, most likely.