At 60 mph in a up hill pull between 2400 to 2700 rpm truck has miss when throttle avance fast. When throttle avance slow truck runs normal. Pulling a load
of about 12000 lbs. No codes - 1999 chev 1 ton 6.5 were do I need to start looking for problem. pmd is located under front bumper for cooling.

I'm far from an expert but from my own experiences, I would be looking at fuel supply. Filter, lift pump and oil pressure switch first.Dan

ensure that the LP and OPS are working correctly and all the time. You can test lift pump by opening petcock on stat housing with truck running. Truck dies you have a problem, if truck stays running as fuel comes out of line good lift pump. Now you need to jump around the lift pump relay, just for a test, and drive it to see if it still misses. You might have to pull your trailer to see if you have found it. If you just want to make sure this isn't it, then there are threads on this site on how to install a relay around the OPS, which you might want to replace at the same time too.

This isn't the same as the miss you had when the WG was stuck?
When you troubleshoot the fuel system, note how much air is bleed from the filter bowl.

Check the accessory belt for stretching, on mine this pulled the tensioner into itself causing a missing feeling.