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Look inside the truck for the leak, it probably left some staining on the firewall and is traveling down under the floor mat.
10psi at idle is actually within specs. It is normal to have lower pressure hot than it is cold due to thinning of the oil as it gets hotter. Otherwise normal causes for low oil pressure include oil pump output, and internal bearing wear. (crankshaft and camshaft)
No, P0301 is a misfire cylinder #1. The secondary air system is part of the emission controls and it delivers air to the exhaust manifolds during a cold start to reduce hydrocarbon emissions and assist in getting the catalytic convertor to work faster.
The problems you are describing would be associated with a loss of communication on the high speed data bus(CAN). What are some of the details about how and when the symptoms occur? How long do you have to drive the truck in both time and miles? Is that consistent with the majority of the occurrences? When it happens, does cycling the key make the problem go away again, or do you have to turn the truck off for some period of time? How likely is the symptom to occur on any given day? Does it happen one or more times a day? A week? Or month? Does the weather seem to have any influence on the symptoms occurrance?
"Dry Gas" doesn't get rid of water in fuel, it simply goes into solution with it and makes it freeze at a lower temperature. The best approach is to forget about just fueling up for the moment and start troubleshooting the misfire like any other event. If the misfire is subsequently proven to be fuel related, then and only then do you get back to the other suspecions. Take note you said that it is raining, this easily could be just a basic ignition system issue and until you test and prove that in or out, anything else is just a guess.
Did someone check the air filter recently? If so make sure that it is latched closed correctly.
The camshaft being out of time (chain worn/jumped) will result in a cranks but won't start, no spark. Unplugging the sensor lets the computer ignore that input and it starts the engine off of the crank sensor alone. A DRBIII scan tool would likely report that the cam/crank signals are out of sync while cranking.
Where did you get the catalyst, and was it CARB OBDII approved?
It's not the convertor. Does the master cylinder have brake fluid in it? Sometimes a brake line fails and it sprays the fluid and doesn't show much of a wet area. If the fluid level is low, add some and have an assistant pump the pedal while you watch underneath. You'll probably find a leak. There is always a chance the master cylinder itself has failed, but they usually cause the pedal to drift down (fade) at stops before it just quits working.
The warning likely means that the tool is not to be used while driving, similar to you shouldn't be texting and driving. It's not going to hurt your car, but the user could hurt him/herself if they try and drive and use the tool at the same time. Right now some tech is going to have a hard time getting to sleep because of that tool missing. Pleae make sure they get it back ASAP.