flat spot off idle when first fired up
 

I have a 1998 GMC Sierra 2WD 6.5 Turbo Diesel. It is my first Diesel, and while I have been twisting wrenches on anything that burns Gasoline since 1962, I'm new at troubleshooting a diesel. The truck has 140,000 miles on it, and is spotless, doesn't burn a drop of oil, but when I first fire it up ifit has been sitting over an hour, as I accelerate from a stop, (gently), it has a flat spot that is quite wide right off idle, after it has been babied for about a tenth of a mile it is fine, I have pulled a ton up a seven mile long steep hill, (800 foot climb), without it missing a lick, and being retired Army, I can't just throw money at it. I think that if it were a bad PMD, the problem would show with the engine at temperature, this happens before the thermostat ever opens. Do I have a lift pump that is fixing to let go? If I need one, I heard that throwing in a 15PSI pump, (Carter for a Dodge), makes it run stronger, but this thing is giving me 20MPG, and I would like to keep that if I could. Living in far west Texas, it is a 200 mile round trip on "Texas Two Lanes" for anything other than Coffee.
THANKS Guys,
Brie