Check engine light ONLY 130 miles from home

I have a 2002 Chevy Express 2500 passenger van with 350 engine. It is used a few days a week around the Rochester, NY area where the terrain is fairly flat and, for the most part there are no long hauls up steep grades. Runs fine locally. Each summer as I travel to the Adirondack mountains, I pull a steep grade up a long hill, starting from a dead stop. This is not a high-altitude area, only maybe 300-500 ft above sea level.

As I go up the hill I notice a loss of power then a downshift to very high RPMs in 2nd gear. Power loss continues and the check engine light comes on. Exhaust stinks. At the top of the hill, after a while, the light goes out. It will also go out if I shut off the engine at the top and restart. My mechanic finds a “random misfire” code. This happens every year as I travel to my favorite lake with a modest load and towing my 14 ft boat. There is no hill locally where I can reproduce this. Minimum drive to a good hill is 1 - 2 hours.

So far my mechanic has changed fuel filter, pcv valve, plugs, wires, coil wire and distributor cap, cleaned corrosion out of the distributor. I have run through two tanks of premium gas with fuel injector cleaner. Again this year, up that hill: “check engine”.

I can ignore this since it is a rare problem, but I have visions of not making it to my favorite Lake some year as I try to haul that hill. Any suggestions on what to do next or even how to induce the problem without driving an hour or two to check it out?

He changed ONE coil wire? Did he test all of them?

Maybe tell him you’ll buy lunch and take him (and some tools) with you up that hill.

Roadrunner: He did say “wires”. By coil wire I think he meant the wire from the coil to the center of the dist. cap.

I think the next step would be to replace the ignition module (“igniter”).

ask your mechanic to check engine manifold vacuum to rule out a exaust/cat concern

I wonder if the problem might be the catalytic converter(s).

Induce problem: drive at that speed, with foot on gas and foot on brake. The engine doesn’t know, and doesn’t care, how the load is done.

This 2002 doesn’t have a HEI? High energy ignition.

I have a 5.3L V8 in my '02 Tahoe and each plug has it’s own coil.