I am caring for my sons car while he is gone and it is a 1996 Chevy Blazer with a 4.2L V6 engine.

He has had a problem from almost the first day with this car. It will run beautifully on most days and then all of a sudden it will start missing a sputtering. He has spent about $1500 on this problem and it still exists. He has changer the fuel pump and filter, which required dropping the gas tank as I recall. All new plug wires, rotor, all that stuff. And still it does it. Now all the time but he says it seems to happen when it is wet or even a day before a rain storm. So he's thinking an humidity connects. Any ideas friends...

I would have thought first spark plug wires, or a cracked distributor cap, or a dying coil.

I ran across this once years ago (in a 350 Camaro, IIRC, and it was none of the above - there was a lot of moisture in the distributor cap. Dried it out and all was well.

But I'd suspect bad injector wires at this stage, or a bad or loose connection at the harness.

"all of a sudden it will start missing a sputtering"
Problem since the CAR was new or since how many miles/years?

Vacuum leak. A broken hose,probably where it females over a male teat. Something - bump, panic stop,..- moves it and it causes problems until it falls back into place.
Yeah, I know; but this is all I can come up with.

Trade it in for a Barth!

My first thought was same as Rusty's.

A plug in code reader would be a good investment now. That vehicle has OBD II, so a good reader reads lots of parameters.

Has he or you sprayed the wiring down with silicone? That often helps. Best done to a warmed-up dry engine.

Like Bill, my first thought was the same as Rusty's, then I remembered having a car with a similiar problem, the fix, after tinkering for months, was replacing the cam shaft sensor.