2007 Frontier LE 4.0 random misfire

Hey everyone,

I got a 2007 Frontier 4.0, 160K with P0300 random misfire during acceleration/load. I had a bunch of problems with the car ever since I took it out of the body shop couple months back. I need to get my smog check done by end of month so I need to get this issue resolved ASAP.

Here's a list of couple things that happened in the past few months...
-body shop replaced my ecu (they said car wouldn't start, and had to replace the ecu). They also replaced my fairly new battery (I wonder if they shorted something out in car). My aftermarket alarm was not flashing the taillights when arming (they end up fixing it somehow).
-after they replaced the ecu, I had a check engine light. Ended up having to replace Ignition coil #1. Drove for about 100 miles, then another check engine light (Ignition coil #3) with (catalyst system efficiency below threshold bank 1). Damaged cat due to driving with misfiring.
-replaced Ignition coil #3, did not replace cat. (was planning to replace cat myself)
-bought cat, but was too lazy to replace for a couple months. Car started flashing check engine light and felt sluggish. Replaced cat finally. No more check engine light but now I'm getting "P0300 random misfire" during hard accelerations.
-changed spark plugs, and did fuel system/intake cleaners. Still same misfire during load.
-car drives fine on light load, but I do hear that 2k rpm knocking sound if I accelerate hard. I'm not sure if I remember hearing the knocking prior to body shop. Is it possible that they put in bad/wrong ecu?


Any ideas or suggestions I can go from here? Thanks!!