In 85+ degree weather my truck loves to stall, stumble and die. 1996 3/4 ton truck.

Had this issue since I bought It 2 year ago but not until recently this summer did it start to get really bad and eventually die on me at a stop sign. Coming up to a stop sign or light I have to two foot the pedals to keep it running. This happens even when I start it up in the morning after sitting all night.
Thought It could have been the injectors, so replaced em and same thing. Replaced the stock overflow valve with a Tork Tek adjustable one and left it at stock setting, same thing. Truck runs great in winter, or whenever its relatively cold outside. I really need some help guys, anything is appreciated.
Replaced fuel filter and fuel skim filter (the one by the lift pump). I did bleed the system correctly. Do not have a fuel pressure gauge yet. Lift pump looks pretty old, going to get one pretty quick here.
I did the whole "cold water on the injector pump" and no change.
Never adjusted the valves, could that be it? Feels like a fuel problem to me.
I heard about a fuel line that goes bad every few years, not sure which one it is though.


Truck info:
1996 ram 2500 12v p7100, stock 47re, 4.10 rear gears (306k miles)

Mods ive done to the truck: (truck was 100% stock when I bought it)
70hp Injectors March 2020 (Ducky fuel injection)
Tork Tek overflow valve March 2020
PDD AFC Live fuel controller with max travel kit
TV cable potentiometer kit
BD diesel noise isolation kit

 

Bump

 

Having this happen after sitting overnight tells me you have a leak somewhere. It could be sucking air into your fuel system while driving. That is what I think the problem could be.
Chucks

 

Thanks for the reply, but this was quite a while ago. Ended up figuring it out, idle was almost x100 rpm lower than it should have been. I bumped that up to about 7 or 800 rpm at the time and it solved my issue. Also, helped it from overheating.

 

I am having the same issue and I end up replacing the lift pump, along with inspecting the entire fuel system for any leaks or blockages.

 

Do you know what the fuel pressure was before changing the overflow valve? I would check the pressure to determine if the lift pump is serviceable. But having said that, If the pump is sucking air, it will show a lower pressure. If you can, look on the top of the tank. If it looks dark in colour and dirty, it can have a small leak where the fuel line connects to the pick up assembly. There is one flexible fuel line that its accessibility is difficult. It connects the steel fuel line to the line to the fuel filter. Rubber lines can fail over time. My return line failed and had difficulty to change it. When my cab was off, I changed the line to the fuel filter with ease. I hope this will help.