Firepuppy, as for your sunroof, I would start with getting a can of compressed air (like you use to clean your keyboard with and then take some masking tape and wrap the end of the straw to make it about a 1/4" diameter in size. Then place the tape ball up against each of the drain lines and use the compressed air to blow out the lines. Once the lines are free, you can then use a hose or a pitcher with water and flush the lines out.
As for the backup sensors, with the engine off (e-brake set), turn the truck to the RUN position and then put the gear selector in R. Get out and walk around to the back of the truck and put your ear up next to each of the backup sensors. You should hear a high pitch chirp/squeak. If you hear it out of 3 of the 4, then silent sensor is the one that is failed. If none of them are making any noise, then the problem lies in the computer box or the fuse for the system has opened. I would also check to make sure that your reverse lights are on. If they are not, then your backup sensor system will not turn on.