[CC69Rat]

So, it ran fine when you took it in for the Exhaust work.

to make sure I am understanding, Midas put the headers AND mufflers on for you?

It's very possible they have a spark plug wire crossed. Have you checked the firing order and made sure your plug wires are on correctly?

the Odd numbered cyl are on the Drivers side. Starting from the front cyl, 1,3,5,7
The Even numbered are on the Pass side. Starting from the front cyl 2,4,6,8

you want to make sure (trace each wire down, make sure you hear it 'click' if you push the plug wire up on the spark plug) The Firing order is 1,8,4,3,6,5,7,2

So, you want to find #1 cyl. (Driver's side front) Trace that wire and find it on the distributor. #1 should be "pointing" pretty close to the #1 cyl. If you drew a line from the dist to #1, comparing it clockwise it should be in the same general area.

Counting clockwise around the distributor, make sure your firing order is 1,8,4,3,6,5,7,2 All the plug wires should follow this sequence and match the cyl it's connected to. It is possible if they installed your headers, they have one crossed. the most common one I have seen is 5 and 7. (I guess because they are right beside each other, and on the same side)

that would definitely cause it to sputter !