I have a 99 f350 7.3 4x4 with just muffler delete pipe on it and an dp tuner, most of the time I run 80 horse econo, but it runs fine while driving, no smoke, plenty of power, no codes or engine light, and has a little blowby, 131,000 miles on it, it seems like after you have been driving for awhile, engine is up to temp, no ac or ac on when you pull up to stop the torque converter disengagues, the rpms will sometimes jump down bout 500 and then back up again to normal idle. it does not die and you do not feel it, but I always watch my gauges, and have noticed it. now today same thing but stopped at a gas station for my wife to get a drink and in park really started shaking, not bad but to notice and almost seemed like a miss, but reved the motor up to bout 1000-1500rpms for 5-10 secs and it cleared out. went about my business and got home and same thing, did same thing and took a little longer for it to clear out, but seemed like the idle was lower, but switched to stock mode and still did it but finally came out of it. checked air filter, oil, coolant, want to change fuel filter maybe the weekend, and drain bowl. other than that always run low sulfer fuel from shell, no bio and will run a can of sea faom through every couple of tanks, other than that fuel mileage has been great 14-16 with 1,000 pound welder in the back, but was wondering if any of you guys have had this prob, or know what to check for. any help to get me pointed in the right directio would be great.
also have gauges, ex temp is fine, and engine temp is
need any more info let me know I am a ex engine builder-mechanic, but am new to the 7.3 truck world, my first one

 

First thing to check is fluids and filters. How many miles on the oil, and is it full? If it's time for a new fuel filter, change it.

Kind of sounds like an oil issue.

 

oil level is full, and maybe 1500 miles on it from last oil change, hpopoil is clean also also and full, gonna change the fuel filter also when I get chance maybe weekend, or if not sooner I get a rain day