Recently purchased at auction a rather ''beat'' '06 F150 XLT w/5.4L, 4x4, automatic. Has plenty of issues... first one I'd like to decipher before putting big money into motor is this: 50% of the time the truck won't start in P, must put it in Neutral. When it does start, it'll rev a bit and when it settles into idle I lose all the dash lights, radio (non-OEM Sony head), odometer, heater/blower/AC, power windows and who knows what else. Headlights stay on as do dash warning lights (check engine, etc.). Truck runs/drives basically fine and if you run for 20+ minutes (nice and warm), occasionally all of the above comes back on while driving - usually only happens at highway speed. Otherwise, from the startup condition, the dash/radio/heater/etc. will come on momentarily when stopping at an intersection. After stopping, when you take off, it shuts down again 95% of the time, the other 5% it will stay on for at least a little while. Another symptom.... dash and guages sometimes quiver and/or make buzzing/ticking sounds when you first put the key in ignition.... and sometimes this stuff even persists after removing key. I think the previous owner had all sorts of funky electronics hooked-up but perhaps didn't remove them correctly (I believe prev. owner was living in a topper camper on the truck...). New battery installed, and it didn't fix/affect the problem.

What am I looking at here? Neutral sensor? GEM? short in steering column? bad stereo install? newbie here all around.... any advice is greatly appreciated.