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Need Diagnosing Help

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What's up guys

I've searched and searched but haven't diagnosed my truck...

For the past two weeks the truck has been back firing/ or shutting off.....


So to get you guys up to speed...I've had a similar issue before but it ended up being the ignition coil and a short at the brake switch....

I've changed plugs, rotor, dist. Cap,wires, serpentine belt, tps, cps, ignition coil, oil, air filter all with in the last month.... o2 sensor in jan,added extra grounds, and done all of cruisers tips, tightened all manifolds bolts


What happened at first afterwork 3pm...was a small bucking and when I got to a stop at idle the truck shuts off, starts up normal and drives the rest of the way normal....it's been like this all last week and the weekend....

until Monday in the morning no symptoms until half way to work which is a 12 mile drive the truck bucks and backfires once at 60 mph and ran normal all the way to work...it's been the same Tuesday and Wednesday and today also but now instead of in the afternoons last week it's only happening in the mornings this week...

What I have been noticing is that theres little bit of a power loss shifting into gears...like a 2-5mph difference shifting into gear I've noticed the engine being revved a little more than usual but not because of my foot but seems like a clogged cat?

But what can be causing the bucking and backfiring on the hwy at 60mph? A relay losing its connection once in a day?


Any diagnoses would help....thanks in advance

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This tripped the old memory switch bringing back an issue we had at the dealership on an 86 4 banger. The guts of the catalytic converter had melted into a softball sized lump and would blow to the back of the cat and plug the exhaust. Symptoms were backfiring, low power. Then the softball must have rolled around a bit until the exhaust pressure pushed it to the back again. What a bear to find. 

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