99 6.5 diesel problems

Hi, I have a 99 k 3500 diesel dually that has 63000 miles on it. I recently towed a travel trailer from Kansas City to northeast Mississippi, the heat was so bad the ac would not cool, I stopped in Arkansas and the truck would not restart until it cooled down, the truck ran in the 240 degree range across I 40 and into Mississippi, I would leave the truck running for about 10 minutes to cool down after the highway drive and then there wasn't much of restarting problems.
Now, a month later, it is starting to have hot start problems, it appears after 10-15 minutes it will struggle to start. I noticed the glow plug lamp is quick triggered, it will come on for about 4 seconds and go off, it takes a long crank to get it started.
Today after setting for about a week I attempted to start it and waited for the glow plug light to quit cycling, it struggled to start and once it did it smoked like a fogging machine, the smoke was gray and it took about 90 seconds to start clearing, Could I be having injector pump problems? I received a letter from GM extending the injector pump warranty. I am tempted to take it into the dealer if it is under warranty but don't want to take it in if it is a dumb operator maintenance problem.
Any ideas would be appreciated... Thanks in advance....

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