Any way to test coil packs?

2004 TB EXT, 4.2L I-6. Steady misfire on a single cyl. Changed spark plugs, (installed A/C Delco Iridium, 41-103). Fired it up, and miss was gone for about 20 seconds, then came back. Scan turned up P0301, Cyl #1 misfire. I picked up a coil pack, but before installing it, is there any diagnostic tests I can do on the connector, or does anyone make a tester for coil packs? Not wanting to install this $80 part, (rendering it non-returnable), and have it make no difference. Hoping to at least be able to check for proper voltage supply and trigger signal at coil connector, if possible. Also, any checks I can perform on the injector harness? Thinking it may be one or the other. Or should I swap coil pack to another cylinder, and see if problem moves with it? Thanks!

My info shows a different coil for each spark plug. Did you visually check for spark at the plug, engine cranking? You can disable fuel, so it won't start.

You could swap the coil to a different spark plug, see if the problem follows the coil. If the problem follows the coil to different spark plug then the coil is faulty.

There are a lot of issues that can cause a misfire code.

I was afraid to test for spark, (using a non-installed plug, inserted into coil wire & grounded against the head), because I had heard the coil packs are really sensitive to the amount of resistance, (including arc gap and ground quality), and can fail when tested this way. So I swapped coil packs for cylinders # 1 & 2, cleared DTC's, drove it for about 3 miles, then scanned it again, and the problem had moved to cyl # 2. So I installed the new coil pack on #2, cleared codes, and the miss went away.:) No more CEL or DTC's after 2 days of regular use.

I will say that I would have wagered the problem was on #1, based on the appearance of the spark plug. It wasn't wet, but it looked somewhat "cold", and a bit sooty, compared to the rest of them.