2001 Suburban 1500. A few weeks back the vehicle started shifting a bit hard into 2nd. Rebuilt the tranny only about 30K ago. Didnt seem right. Within days I started getting a very mild misfire. After a week or so the misfire started getting bad and the check engine light came on. I went and got the codes. They are as follows.

P0300 Random/Multiple cylinder misfire
P0446 EVAP Vent solenoid valve control system

Secondary DTC's
P0161 HO2S Heater performance Bank 2 Sensor 2
P0171 Fuel trim system lean bank 1
P0174 Fuel trim system lean bank 2
P0327 Knock sensor circuit low voltage
P0332 Knock sensor 2 circuit low voltage bank 2
P0446 EVAP vent solenoid valve control system
P01258 Engine coolant overtemperature - protection mode active

Fix finder diagnostics program suggested replacing the fuel injector pressure regulator. I did that. Did not fix it. On my test drive the battery light came on and the fuel gauge went to E. I put 10 gallons of fuel to make sure that it should be reading. Still on E. Drove home. Checked the battery voltage at rest and got 12.6 volts. Alternator 14.55 volts when running.

I figured the fuel level float is attached to to fuel pump, so I replaced that. I knew it may be a long shot and I was right. Didn't fix anything. On my next test drive it was still shifting hard into 2nd, still misfiring, battery light on, fuel gauge not working, then the odometer screen blacked out and the interior vent fans quit working.

Now I'm thinking bad ground somewhere. I took apart and cleaned up the 3 grounds on the body by the firewall, the one on the driver's side of the engine block and the one behind the front bumper. There is one on the back of the block that i could not get to, but by yanking on the cable it looks and feels solid. None of these were the issue.

I'm stumped. I was thinking maybe the ECM/PCM, but if I'm right those have nothing to do with the interior electronics. I don't know. I just stumble my way through this stuff. If anyone has some insight I would be very grateful. I have extra vehicles but this is the one that holds my whole family. Thanks for taking the time to read this.