Catalytic Converter keeps going bad.

[KSE_rules]

I have a 2007 Limited v8 4wd Explorer
To start everything off, I was having transmission problems December of last year (2015). Slipping and hesitation and whatnot. Rumble in gear at constant speeds.
I brought it to a shop and they "rebuilt" the transmission. They also told me the cat was bad and if I bought one they would install it for free since they were already under the car there.
So I get it back about a week later and its better than it was but transmission still feels kinda iffy. But I figured it had a lifetime warranty and I needed the vehicle back.
Well now 7 months later the transmission has been acting up like crazy and even seemed to have gotten stuck in a gear once. Not 100% sure since the Misses was driving.
So I brought it back to the shop and they "rebuilt" the transmission again under warranty.
Well they called and said my catalytic converter is bad. I told them I had bought a new one and they installed it in December. Apparently this one is clogged/bad too.
They unbolted the cats and I drove it home. It shifted fine but obviously with no back pressure it drove like crap.
I want to just bolt these back up for now but I need to find out what's causing the problem to the cat.
I'm trying to give all the details however irrelevant just incase it might provide some sort of insight.
So I'm thinking it's either dumping too much fuel and running rich. Or the exhaust is heating up and destroying the cat.
Any suggestions would be amazing. Thank you guys!!!

 

[Spades]

Do you have a CEL codes? If not, then maybe their pulling your leg on the CAT since they had to repair the tranny under warranty and they want some kind of $$ out of you. What were they doing inspecting your cat anyway since it was in for tranny service? And besides, the cats should be warrantied too, they installed it only months ago

 

[KSE_rules]

Right now there is a bunch of check engine codes because the exhaust isn't hooked up. All of them are 02 sensors or running lean/rich.
I bought the catalytic converter online, brought it to them and they installed it for free. My only concern is that did they even install the new one?
Looking under the truck the cat looks like it's old. I honestly can't remember what it looked like when I bought it.
I'm going to try contacting the manufacturer and seeing if they have any sort of markings on it that would designate that it's theirs or not.

 

[KSE_rules]

So I finally figured out the problem. Probably about two weeks ago. Usually I forget to post updates to anything like this so just in case someone had something similar.
I ended up changing the spark plugs and fixing all the problems.
One of the eight was broken off inside. Not sure if it was already like that or if it happened when I was removing it. Either way it fixed all the problems.
The truck shifts great, has all power. Seems to start easier. Ymmv.
All in all wasn't horrible to do either. The one plug did take a while to do because it came apart and I had to rent the tool for it.