Sudden loss of power - 3.9L V6 Magnum RAM Van

After borrowing the Van to a friend for a short trip we begun to notice a significant loss of power and performance. Previous performance was satisfactory given the van's weight/aerodynamics.

Now the van cannot go over 75mph, pedal to the floor. The higher the speed, the less response you can get from acceleration.

Any idea where I should look first to tackle this problem?

Engine is a 3.9L V6 Magnum. It had some problems starting when cold - I had to give it gas to keep it from dying - that were solved after I cleaned-up the IAC and idle air passages. There are no error codes stored in the PCM.

Take a fuel pressure reading. I suspect that either the fuel pump is weak or the catalytic converter is clogged.

What about dragging brakes? I loaned my '96 B2500 to my bro-in-law and he crammed on the parking brake so hard that it wouldn't release all the way...(probably a sticky cable or rear shoe on the backing plate...never did figure it out...it went away). You never know what someone else will do to your Van. I wonder what gas your friend put in it before he brought it back??? Alloro, the fuel issue is probably an easy starting point. My CAT is rattling and I'm worried about it getting plugged up, but so far no power/MPG/idle issues.

This van has a second LPG fuel system installed along the factory system and the problem is the same on both - we can rule out the fuel pump.

I've noticed a batch of misfires when the van starts to stumble and on idle after that. On high-RPS's it smooths-out so I wonder if the cat is the problem... I never had a cat failure until now but I imagine that high-rpm's should be a problem with a clogged cat.

The brakes are fine - car can coast for miles if you don't mess with the brake pedal. I suspect if we don't have a failure in the ignition system (coil, rotor, cap, or wires). Van showns no error codes yet but something is obviously wrong.

Interesting problem, especially since the PCM hasn't thrown you any codes. I had a starting/idle/power problem in my '96 B2500 5.9 EFI V-8....never showed a code, but
problem eventually turned out to be a faulty/intermittent temperature sensor (NOT
the temp. gauge one, the Other one that reads electrically to the PCM). You might take a look at that sensor on your V-6. Not sure how to test, but Alloro could maybe help you. The sensor was telling the PCM that engine condidions were different than
they were, causing bad feedback to PCM and therefore bad run conditions to rest of the FI circuits, hence the Van ran like crap. Just an idea....good luck.

Found a scuffed spark plug wire and changed the dist. cap. rotor, spark plugs & wires with a quality set and thrown in a MSD coil for good measure. Now performance comes and goes, one day it pulls great when you press on the gas pedal, the other it's sluggish and slow in taking off from a stop.

New development after the tune-up - at first start if you try to take off right away the engine misfires and has no acceleration. After a few minutes it behaves more or less normal.

Airflow and exhaust are good, no fouled plugs, clean tailpipe but performance is like we're burning hot air instead of gasoline... Any idea on what to try next?

I'm thinking about TPS or Oxygen Sensors but I don't know if those could cause this kind of issues.