Hi. This will be lengthy so thanks for reading. I'll try to be both concise and brief. My OBDII troubleshooting experience is mostly with a 97 LT1 car. Troubleshooting an LS is entirely new to me.

07 TBSS completely stock, 120k on the clock. Daily driver, has run great for most of the 3 years I've owned it.

It started dying in traffic and at random, set a code 1682. Replaced the ignition switch. Problem ended up being the fuse box. It needed control arms and exhaust manifold gaskets/bolts, so I took it down for a week or so while I was doing all of the repairs.

I had to disassemble the air box and plumbing to get working access to the passenger side manifold and bolts. Cleaned the MAF and throttle body while it was all apart. Used CRC MAF&TB cleaner.

Completed repairs of upper & lower control arms, both exhaust manifold gaskets/bolts, fuse box, and replaced plugs/wires while they were off anyway. Delco wires and ACDelco 41-985 plugs, as far as I can tell the closest thing to stock with a superceded part number.

First start after reassembly didn't go well. It barely ran and I got to the end of the drive and back with it. It set codes P0449, U0101, B2AAA, and P0306. I had missed a prong with one of my copper leads, and had to redo my fuse box repair.

Next test drive was great. Ran great for a few days, then it set the P0306 again, and started occasionally hitting hard with the Park-Reverse shift and the 1-2 shift. Just a couple times when cold, then smooths out. Motor runs perfectly. No way it's missing a cylinder.

Switched (over time, individually), the plug, wire, coil, and injector from #6 to #4. No change. Still sets P0306 code intermittently. It may run fine and set no codes for a few days, then have the engine light on for a few days. Hard shifts are also intermittent, but are always only upon cold-ish start. Once you've driven it a mile, it shifts normally in every way. However, there are times that it shifts fine even first cold start for the day.

Out of frustration and guesswork I replaced the fuse box with a new one. Thought maybe it was having an intermittent short again because of my repairs. New fuse box made no difference.

I do not have a scanner that specifically checks for transmission codes, so I do not know if it's setting transmission codes. P0306 is the only code it sets. Sometimes it will soft code for a few days before it turns the engine light on.

Freeze Frame Data from most recent P0306:

Freeze frame report generated by Torque for Android

Vehicle VIN: 666
Vehicle Manufacturer: Chevrolet
Vehicle Calibration ID: 126

Freeze frame information:
Fuel Level (From Engine ECU) = 53.333 %
Distance travelled since codes cleared = 82.021 miles
Evap System Vapour Pressure = 5.25 Pa
Barometric pressure (from vehicle) = 14.794 psi
Catalyst Temperature (Bank 1,Sensor 1) = 851 F
Catalyst Temperature (Bank 2,Sensor 1) = 851 F
Voltage (Control Module) = 14.343 V
Engine Load(Absolute) = 24.706 %
Commanded Equivalence Ratio(lambda) = 1
Relative Throttle Position = 8.627 %
Ambient air temp = 80.6 F
Absolute Throttle Position B = 23.529 %
Accelerator PedalPosition D = 20 %
Accelerator PedalPosition E = 20 %

End of report.

I'm still daily driving it. I have no idea where to start troubleshooting next, as it's all intermittent. I double checked the TB and MAF plugs, and they appear visually undamaged and tightly connected. I'm sure someone will tell me to do a compression test, but given that it's an intermittent code with no driveability symptoms, I can't imagine it's anything mechanical or that a cold compression test in the garage will catch the random conditions that are setting the code. I'm certainly all ears.

Thanks again for reading.