That is definitely a sign! Your hand on the bracket should not have given you a shock. It should be solidly grounded to the engine.

However, even given a loose mounting bolt, your coil Outer insulation is probably bad. Have someone crank it while it's dark, or even just run it while dark, you'll probably see random sparking.

For what it's worth, a guy that I work with had a prob with his.. funny enough I never asked what the real problem was, but just laughed because every time it would rain he'd put a plastic bag under his pass side w/shield wiper, and let it lay over the firewall/top edge of hood. He said that something gets wet & it won't start if he didn't do it.

He no longer has the Blazer.. the kind of guy goes through a car a year. Whenever something goes wrong he doesn't fix it, but just calls it a POS & moves on to something else. Last I saw it, the front stabilizer bar was dragging on the ground. I pointed it out to him, and he says "Huh. I don't care, I'm trading it in anyway".

I have this problem with no start when it has rained.
 

1999 freshly rebuilt motor, new injectors,fuel filter, battery, plugs and wires. I have another coil, module and distributor from another working blazer to test with. I'm going to swap them tomorrow. I'll do the coil and module first. I'll post my results.

Sounds like your coil is NOT grounded. I have replaced a few of them on the 4.3 and they are just rivioted (sp) on and they get a lot of oxidation around the riviots. Go on and get a new one from Jegs in Columbus Ohio. They will sell you am MSD coil for about the same price other stores do. Then when you get it clean the bracket good on the sides that touch the coil. Put a little grease on it too just to keep the oxidation down. I don't know why GM didn't put a grounding lug on their coils. Jegs 800-345-4545 coil part number 121-8231 this is for a 96-97 4.3 cost was 40.99. Make sure you tell them the year of your Blazer, just to get thr right part. Cold wet ( hard starts) Replace the plastic dist with a good metal one. You can't get the screws tight enough on the factory plastic dist. to keep moisture out. If you need one I have a great supplier on them cheap too.

Just a word of caution on the MSD Coils, I have seen a number fail in EDI GM systems.

As far as the distributor goes, plastic or metal, both are open on the bottom, not sealed so you only need to tighten the cap down enough to keep it from moving around. You don't have to meat fist the screws attempting to get a water tight seal. If it was meant to be sealed, it would have a gasket or o-ring.

As others have stated, this stinks of ignition system problems. Mist down the top of the engine at night & look for arcing from the wires. If there is spark escaping, then the component it is escaping from is not working properly.

As with a lot of things on these trucks, aftermarket parts generally suck. The ignition system is definitely not something to go with bargain bin components. Many people have chased ignition system problems spending hundreds of dollars only to find that the $20 cap/rotor/wires/etc they bought was faulty just like the old one that it replaced.