200K on this truck, driving down the road it acted like a cylinder stopped but drove it home, hired a mobile mechanic who replaced all plugs, wires, ignition coil, pcv valve, fuel filter..now it runs good at 2500 rpms or more, but chokes and dies below that, bad smell as well. What to check next??

 

Will try the carb cleaner to see if vacuum leak next....

 

No response at all with the carb cleaner, sprayed around all hoses, engine running..