start small then work your way up, check to see that the coil for 5 and 6 is being triggered, connect a non powered test light to the positive battery cable, then back probe the ground wire for each coil, if its being triggered and you can confirm it has spark, then check that those injectors are being triggered
if they are both being triggered, i think i already said this, do a compression test
test all cylinders for comparison, they shouldn't vary by more than 10%
if 5 and 6 are low, you might have a blown head gasket