Welcome to DieselPlace
I moved your post over to the 6.5L section of the forum for better views and responses to your issues and questions.
I would start by checking for any codes the ECM may have recorded.
You can check for codes using a paperclip and follow the info in this link:
If you do have any please post them here.
1996 K3500 6.5L,( "F" Eng #141 cast block) 5 speed manual, crewcab, dually longbed: 208,000mi.
Diamond Eye 4" Turbo Back Exhaust w/2.5" Flo-Pro Crossover
AirDog II DF165 w/ tank sock delete - XDP
TD-Max boost controller - Kennedy Diesel
OPS extension hose - Leroy Diesel
Glow Plug Harness- PT Wiring Solutions
Glowshift Maxtow EGT,Boost, Fuel gauges
Boost & Fuel Pressure Bolts - Leroy Diesel
2/0 Battery Cable Upgrade - PT Wiring Solutions
PMD w/#9 resistor and Re-Location Kit, mounted to bumper - Leroy Diesel
4.10 gear ratio
OptiLube Winter Formula
Proud member #1039 of The 3500 Dually Club