Hello I got 1998 ram 5.9 magnum.This past winter I rebuild the motor, put it in, drove normal for few weeks then went to parents place grabbed car hauler with 2 round bales (around 4-5k pounds). Drove out, drove about half a mile and reached about 70km/h and it started to bog down, I stoped, turned around and barely made it to parents yard, no power at all. At the yard I dropped the trailer shut it off and was looking around for few minutes, started it and it ran fine. Drove with out trailer for about 7 minutes same thing happened shut it off and cool it down for few minutes, start it up and fine again. So I made it back home like that with few stops. Next morning same thing drives absolutely fine full power, but warms up and bogs down like crazy.So I left it alone for a month or so till I had time to work on it, and it was much warmer outside already. I started it up drove again for few minutes same thing happened but now it already didn't help cooling it down.I started it next morning no power right of the start, bogs down, rough idle, stalls, and you pretty much can't even move it of the spot, start driving it and it will stall.And then it was already hard to start it, if you can get it started when it's cold, runs very rough and soon as it warms up a bit it eventually dies, and after it dies it's almost impossible to start it back up till it cools right down.Throttling never helped and does not, only makes it worse. When you throttle it makes like shocking roar sound. Also there is a loud hissing sound coming from intake that I don't remember hearing before. But there is no vacuum leak at all, I checked all the hoses and valves everything is good!So I pulled the plugs, look very wet, strong gas smell as if the motor is flooding. Did compression test, then I removed the plenum as I thought maybe I pinched the gasket on it and it blew under load? But no everything was fine and now I put it all back together with new gaskets, new distributor, new spark wires, new coil, new spark plugs, new IAC, new TPS and new MAP. Still same problem.No DTCs showing.Thinking of maybe changing the O2 sensor and coolant temperature sensor but it's showing on the dash that the temperature is going up when it rough idles for few minutes so not sure what to do at where to go now. Any help is much appreciated!!! Thanks

 

Verify fuel pressure, if that checks out, pull the front O2 sensor, and see if it runs any better. (physically remove it from the exhaust.)

 

I'd do another thorough check of all hoses, it might be a possible vacuum leak after all.

 

Thank you very much for your help, I checked the fuel pressure it's 47-48psi, and then I tried for about 30 min to take that 02 sensor out, no luck. But then I just disconnected one side of the exhaust from the header and started the truck with absolutely no problem! Pedal to the floor it revs and runs nicely (other than it was super loud) took cat out, cut it open and the front part of the cat was broken in pieces and small particles like sand and the rear part was all plugged as well. Cleaned it out, welded back up, put it back it and drove it. The problem is gone!!! I just need to take it to the dealership to have my fuel timing set? And I should be done.
Thanks again!!!

 

If you didn't move the distributor, you should be all set.