just a thought, ive got a ddx318 (lower end doubledin compared to the excelons) I had it in my 2004 4runner, every once in awhile if I hit a big enough bump it would cut off and I couldnt for the life of me figure out why. After i bought my 02 wrx and installed it i NEVER had the issue again with that unit.
Fuses and everything else was good, i had to reset the cars power by turning the key to the right, which you can do in that generation 4runner (if you turn the key again in the wrx if the cars already running i believe the starter would engage)
The only thing that changed was that I removed the bypass relay (which allows you to have dvds play while the car is in drive, i had that setup so my little cousins can watch their movies if we went on long drive in the lcds i had in the back). I check out the relay turns out it was faulty AND some some of the wires werent connected properly (to the 4runner harness). Maybe if there was a bypass wired up that could be your problem?