Appreciate some help on this one.

I have a 1996 Blazer 4WD. It always runs great, I don't feel any misfires. Let me explain.

Background:
I have had the Blazer for 2 years. About 9 months ago I was pulling a trailer on a long trip and when I started going up a steeper grade, the SES would flash, then set on solid. I did not feel any misfires. Bought a scanner, found the P0300 code set. Trying to investigate the problem, I noticed a tie-wrap on the distributor cap... When I looked further, it was HOLDING the cap down as one of the lugs had broken on the distributor (guess I can thank the previous owner or the place I bought it from). Easier fix than replacing the distributor I guess

So, once I found this I replaced the distributor, cap and rotor with a new one. It ran great for a couple thousand miles, even tested with a trailer on a hill (unfortunately not as big of hill as I should have).

A couple weeks ago:
I had to pull a trailer on a long 200 mi. trip again (I would estimate the trailer/load at about 2000-2500 lbs). Sure enough, same hill, same flashing SES, then solid SES. This time I had my scanner with me. Guess what. P0300 again. I did not FEEL any misfires. I re-set the code. No problem again until another big hill (and mountains). Never actually felt a misfire, had to keep re-setting the code though. I did find it was better when I kept in in 3rd instead of OD and tried not to hold my speed as steady on the hills letting it drop off a bit. Drove all the way home without any codes running in OD, but with no trailer.

I know there are lots of places to check to resolve the problem. I did order a new coil and set of spark plug wires and will put them on when they arrive. Unfortunately I won't know if it helps until I have a heavy load to pull again...up steep hills.

I do recall when searching this problem the first time that I saw something on a Chevrolet service bulletin when getting the P0300 code pulling a heavy load on hills. I think it had to do with valves sticking. Now I can't find that service bulletin in my searches. Does anyone have a pointer to that service bulletin?