Please list all that has been done


Ok like tune up new plugs are the wires good cap rotor replaced be specific as to what has been tried please.


Have you tried some in gas tank cleaners for the fuel system it usually takes about two full tanks of gas and cleaner to work?


Tried some seafoam down the throttle body that's a cleaner you don't need to ad it to your oil unless you plan to change your oil anytime soon. You don't always get the white smoke

How To SeaFoam Your Car The Right Way - YouTube

 

Spark plugs and wires have been changed, also put sea foam in gas tank , replaced both speed sensors, cleaned out cat, that's all that's been done , it's not giving a check engine light, it's backfiring thru the tailpipe, the speed hand jumps from 0 to 120 then the truck stumbles, backfires and then dies

 

Did you replace any O2 sensors?

Is your coolant temp sensor working showing how hot/cool your engine is?

As a start replace your tps (throttle position sensor) they are cheap and usually go out around this time around $35.


Make sure to get a quality tps cheap ones are JUNK

A good throttle body cleaning is recommended but its not easy on the 3.9 engine by good cleaning I mean pull it off and clean it.

Can you pull the air hat that sits on the throttle body off and look down it to see if its very oily inside if so the plenum may be the problem or part of the problem.


One more possibility is the map sensor has an air leak or going bad.