I have a 1995 gmc k2500 with 330 000 km. Starts right up when it's cold or hot and will idle for hours without missing a beat. Lately it has developed what I can describe has running rough at speeds of over 50 km/h. I've swapped out the pmd, no change. Running idle, I've open the drain valve and no stalling and also put a fuel pressure gage which shows between 5-7 at idle. The next logical step in my opinion would be change the injectors but I don't get white, blue or black smoke when I hammer the peddle. Anybody experience the same issue and what was your fix?