Have not had the truck very long had intermediate miss while in park. Does not seem to do it in drive. Put fuel additive in truck drove it 500 miles no miss added 4" exhaust and Edge easy chip still no miss. Drove it 1000 miles put FASS lift pump on and fuel gauge. Truck starts at 20 lbs fuel pressure and 17 lbs at 70 mph. Now it is missing again when hot comes and goes, sometimes won't do it for 2 to 3 days. Put fuel additive in again miss stoped for a little while then started up again. Took to shop mechanic put scanner on it no codes. Any ideas where to start looking for problem?

 

https://www.bluechipdiesel.com/vp44_diagnostics.html

About 3/4 of the way down the page you will find a rough idle section