Installed the 28-pin socket in my PM6 and reinstalled the stock chip. I pluggled it in the car and it does not rev past 4000 and splutters when I rev.

Where did I go wrong?

Is (a) my soldered connections are bad
(b) my stock chip is screwed

 

Could be a lot of different things. You could have fouled one of the traces, dripped solder and shorted something. Just get some desoldering braid and start again, this time, pay extreme attention to what you're doing. If you lift a trace, I have seen Joesph recommends "jump wires".