Misfire in cyl 7 on 2007 Suburban 1500 4x4 with 5.3 L flex fuel LTZ

2007 Suburban 1500 4×4 with 5.3 L flex fuel LTZ 267,000+ miles.
Having trouble with running rough and misfire. The ODB II indicates P0307.

Checked wires – replaced though nothing is wrong, no change
Checked spark output with spark detector – solid steady spark
Plug looked wet, but with oil
Checked oil, 1 qt too high so removed 1 qt – no affect solid misfire.

Listened to all 8 injectors – all sound the same
Pulled all 8 spark plugs and commenced compression check on #7 – over 300 psi
Cylinder was overloaded with fuel and spewed gas out of pressure release of the tester.

Ran the engine starter with all 8 plugs out until gas quit coming out of #7
Compression check #7 = 145 psi, #1 = 150 psi, remainder were 185 – 192 psi
Reinstalled plugs after burning oil off of #7 plug with #1 in #7 position. Restart has solid misfire on #7

Remove power plug from spark generator for #7 – no affect, tried several others and they all made obvious difference in operation, but no change for #7

Pulled rail and interchanged #6 and #7 injectors (inspection has nothing obviously wrong), put back together and started engine – solid misfire on #7 only – tested by pulling connectors on spark generator of each.

Wires are new, plugs are 8,000 miles old, #7 cylinder had AFM lifter stuck and was replaced 8,000 miles ago as stop-gap measure to keep daughter’s car running.

Have 10W-30 on last change and someone added two quarts when it only needed 1/2 qt. I removed a quart so the dipstick now shows at the top of the crosshatch.

Any idea what could be wrong? I am planning to pay to have someone put a new type of testing of equipment on to see what is happening. What should they be looking for?

Thanks!