What causes post timing chain replacement (all 3) severe power loss condition?

[Zap-Trac]

Timing chain let go about a half mile from home; surprisingly enough, I made it home with vehicle barely running. Shut it off in the driveway and she wouldn't restart, understandably. Contacted a local engine shop and had it towed there. Of course there were "complications" upon restart at the shop. Shop manager called and asked all the right questions, pulled the engine out a second time and did a "valve job". New serpentine belt/thermostat housing/spark plugs and new fuel injectors(6). You would think that would've taken care of the problem.
Took it out today and again barely made it home! Was driving along fine, went to accelerate, heard something go "BOOF" from underneath as a blackish/brownish cloud came out the back, engine light comes on steady and I was almost "dead in the water" with SEVERE power loss. The vehicle didn't want to go faster than (approx)20mph !
I have heard that the ECU can go into "survival mode" !? Has anyone else ever heard of this?? I am thinking and checking out ALL possibilities; even the tranny was fine before all this.
Kinda upsetting , any help would be appreciated! Thanks- Z

 

[Todd Z]

Honestly sounds like a backfire and a hose blew off or something let go.... Have to look around and see.... Can be anything from the exhaust to the cooling system...

 

[RodMac]

check you catalytic converters sounds like a back pressure issue. I had it happen to mine. When it would not go faster I assume you had gas peddle to the floor and 20 is all it would go.

 

[Zap-Trac]

Thanks to all respondents, I appreciate your feedback. She's back at the shop that "fixed" her the first time; as is proper protocol. In good conscience, I have to afford the shop the "opportunity" to do the right thing. Hopefully it was just mis-timed. Never thought about the catalytic converter "clogged" as an issue. Phone call tomorrow, anticipating good news; I will keep you posted. Thanks again!
Regards, Z