2006 ram 3500 new to me. 3rd owner. I am having cooling system issues but am about to flush radiatir wind see what happens. I have no way to find out what has or has not been replaced on this truck. What should I look for to see if the lift pump has been changed?

 

With the truck running do you hear the pump running in the fuel tank? if yes then not changed. Check along the frame rails to see if there is a fuel system added, should be easy to spot. Under the hood drivers side look for blue 1/2" colored fuel lines going directly to cp3, if not there, no upgrade. Do you have gauges? Fuel pressure at idle 10psi or less = oem pump, over 10 closer to 15 or above = aftermarket pump.
Hope that helps a little.