I have an 03 4WD Tundra with a TRD SC. The truck has 126000 miles. I was recently pulling a small camper going up a grade and the truck started missing and lost power. The check engine light came on, and when I tried to accelerate it would start blinking and have no power. I took it to a mechanic friend of mine who ran the codes. It was showing P0301, P0302, P0307, P0031, and P0504. The first three was showing a misfire on 1, 3, and 7. The P0031 was an O2 sensor Bank one, sensor one. The last code was the brake light switch. To try and correct the misfire, I changed out the spark plugs for NGK, and there was no change. Next I checked and replaced the coil packs, still with no change. So next I tried filling the tank with 93 octane and added Seafoam. I tried driving it to see if it would clear up the injectors but it didn't. My next option is to replace the injectors. I listened to each one and they seem to be performing consistently, but I couldn't tell anything else. I can't keep throwing money at it hoping to find the problem. Does anyone have any suggestions? I appreciate the help!