Well after replacing that solenoid about 2 weeks ago the truck got stuck in park today when leaving work, with the same symptoms as before (press on brakepedal but cannot pull trigger on gear shifter). I played around with it for a couple minutes and then finally I heard the solenoid move and was able to pull the trigger.
I am not sure as to what else it might be, it could be the brake switch but it seems to be working perfectly fine (brake lights come on, cruise control disengages etc...) so I am at a loss right now. I could tape the plastic component forward which would allow me to take the truck out of park at any point, but I am not too keen on that one as its not really a proper fix. Sometimes though it seems that while I am pressing on the brake pedal I can hear the solenoid actuate in and out 2-3 times without taking my foot off the pedal, so this leads me to believe that there is an electrical issue somewhere.
Are there any other sensors/relays that I should look into other than the brake switch? Or should that be the first thing to be replaced?
Looking at the diagram provided by ornery, Note that the solenoid (upper right quadrant of brake shift interlock circuit) requires three things to operate. It requires 12v from the run start relay in via pin "1". And it requires GRD from the park detect switch in via pin 6. And pin 8 requires a voltage (logic level from smart junction box) through the resistor and to the transistor's base in order to conduct the GRD from the park detect switch. If all three are present the solenoid will operate, unless the solenoid is defective.
The solenoid can be checked with an OHM meter for proper resistance through its windings. Since, you may still have the one you replaced, check them both and compare resistance. And if you provide GRD and 12V it should operate consistently.
Applying GRD to the input (pin 6) of the park detect switch should verify it is conducting. Or check the park detect switch with an ohm meter for continuity.
If you provide GRD directly to the GRD side of the solenoid and it operates, then provide GRD to the output of the park detect switch (input to the transistor's collector) and it does not operate, then the problem is with the signal coming in on pin 8 from the smart junction box.
Replace any defective parts and check wires and connections as appropriate.
Also, it seems very unlikely that the transmission needs to be lowered to replace the solenoid or brake shift interlock in its entirety.
One more thing, when I had a problem with moving the shifter out of park, back in 2007, I discovered that if I held the shifter (either forward or back, I cannot remember) I could press the brake and it would work every time. It was under warranty, so I am not sure what they replaced at that time, but It appeared to have been a mechanical issue, not an electrical issue when that happened to mine. Just something else to consider.