'99 Yukon 95k miles, 5.7, 1500 4x4 Getting P0300 & P0307 codes. Reading it with Car Code via laptop. Misfires showing up in cylinders 7 and 2 mostly. New NAPA premium cap, rotor, wires and AC plugs installed, no change from OEM old stuff. Wires old & new ohm'ed out well in spec. . Misfire only happens when revs are up, are erratic and not steady like a dead plug. With open old school spark tester you can see spark drop out and come back erratically when revved up. (only checked #7 that way) I'm thinking coil is breaking down at higher revs. Idle is dead smooth, no misfire until it's over 1k rpm. Looking for opinions as I don't want to swap out expensive electrics that I don't need.
TIA John