on top of what fish suggested i would check the power at the lockoff solenoid and make sure the power is coming on every time and voltage is good (battery volts).
If the power is good then the solenoid is probably worn to the point it is binding, there is no way to repair this so replacing the lockoff should fix that issue.

Now the throttle issue can either be the throttle body or the pedal sensor (if this truck has that setup on it). Being that it is erratic i would check the wiring and connectors, check the wires going into the throttle body and make sure they are not broken where they go into it, they are known to break there. The other thing about the throttle bodies is the internal connection on the wipers can get dirty and cause a no response issue or maybe even a bad signal making it go high rpm. Also before you get into all that make sure the frame ground is good, clean it if need be, if there is paint under the terminal on the frame scrape it off to bare metal.

Now with all that said you can do a diagnostic using the 4pin diagnostic plug, it will have each terminal labeled A B C and D, you can use a jumper and jump the A and B terminals to enable the diagnostic mode. When you start that the engine light will flash a code 12 three times, then a pause then it will start flashing any stored/active codes in memory. If you're not familiar with this diagnostic test i can send you some info on how that works, just use my email in my signature. You'll want to know if there are any codes before you get too far into it.