Check for leaks around your ram air box. You may be developing a leak only when you're at high rpms ,Causing your air meter to wig out. Like maybe around your connections.something similar happened to me when my cold air intake had rubbed a hole in the ninety coming off of my throttlebody.
2000 Chevrolet Silverado, 4.8L, K&N polished intake, 4.10 gears, 20x9 KMC SS on front, 22x10 on rear, Dual style pillar gauges, steel cowl hood, 2" rear drop shackles, true duals w/IMCO extreme mufflers w/dumps at rear end, SLP headers. Cam and nelson tune soon to come!!!!!