2006 Cadillac CTS jumps when accelerating under load

I have a 2006 CTS, 3.6. 128k miles. Always changed the oil myself at 3,000 miles religiously. A few months ago, the car began to “jump” or hesitate when accellerator pushed. Not right away, but after car reached about 30 mph. Again when on it reached about60 mph on highway. It cruises fine, but if you push it, it stutters a bit and the check engine light flashes, Then regains it’s composure and away it goes. I noticed that when I changed the oil, the filter is filthy, filthy. Always has been. Use the right oil and all. Now, I take it to a local national automotive chain and they tell me it is misfiring on #6 and needs plugs, coils and the works. So I had them do it. The car still jumps at same intervals. So i take it back and now it is misfiring on ALL plugs ( or so the computer says). Now the mechanic tells me that the timing chains are all buggered up and the engine needs to be replaced. So I seek another it to another garage and they say that they see the same codes, but don’t think it is in need of new engine. They would like to keep it anid see if they can find the problem. A week passes and they can’t diagnose the problem (they didn’t charge me thank goodness). Now I am at a quandary. Any suggestions?

Oh, also have a 2013 Acadia Denali with same 3.6L . Drove it to a wedding in Colorado last year. It got hot going through the mountains. Took it to Cadillac dealer and they said that it was actually the transmission getting hot. Asked if I was pulling a trail or something. I said no, but did have an extended cargo ramp off the hitch for luggage. They suggested I put on an external transmission cooling system. So I did, looks like a small radiator for the transmission. It runs great and have never had another problem.

Anytime a Check Engine light flashes it indicates a major misfire.

A major misfire can be caused by all sorts of things. But you need to find out why the major misfire is occurring. Because if you don’t, it’ll destroy the catalytic converter(s)