[AZKen]

As most do, you are mixing drag strip/race motors with everyday motors. Spark is one factor on high compression, high RPM motors. You are in love with an idea that has no basis on a GMC truck motor. He is not looking for .001 second, he is trying to get up a hill. With a 3400-4000 max RPM motor. With all due respect to your experience, MSD style, multi spark, hot coil suggestions, for this fellow, are bad advice and a waste of money.
HEI is a good upgrade as well as a good coil. All of these will probably last longer and start better in cold weather. They may help with fouling, but fouling has a root cause. They won't get a big truck up a hill faster.
Just to let you know, you are not talking to a young kid, I'm 71 3/4. I do respect your opinion and will leave it to the poster and the other members to help decide the best troubleshoot approach. I think some are thinking the motor, with whatever mileage it has, is giving all it has. The weight, grade of hill, gearing= maxed out.
The "extra" spark issue is not supported by others on the internet.