Hey Z.,
I am not sure from your post, does he have trouble reading and writing or does he just not like it? I would also ask you if his handwriting and planning skills are poor. If you answer yes, then I would suggest that you look into an educational evaluation, which you will have to get privately, but will be worth every penny if you find something.
Since he is in a gifted program, ask to see the standardized evaluations that they used to identify him, if he has a large difference between his acheivement scores in language arts and math/science, and more importantly, if they did general intellegence testing and he has big differences between his verbal and performance scores or has more big ups and downs between the IQ subtests, this could suggest some learning difficulties that will cause him stress and frustration. Even if all the scores are higher than average, big differences between them can cause problems and you should know where these are.
I would not venture to guess what the difficulty could be, there are many that manefest this way, dyslexia is one, but dysgraphia, visual motor/visual perceptual, and a whole slew of processing disorders can cause a simualr outcome with very different causes. You will have more sucess helping him if you target what is causing his reluctance to read and write. If he is not behind his peers, he may be functioning below his own IQ level, which is a problem, and if he is resistant, he may also fall behind later.
I am concerned about how early his identification for GT services is, 3rd grade is a little soon for the testing to be reliable. There is some school of thought that 4th grade is the earliest time for the onset of gifted instruction as some kids develop the early learning skills quickly but the majority of these kids will level off with the rest of the class by the end of 3rd grade, making the pool of those kids who are identified as gifted much smaller. If your school has more than 6%-10% identified school wide (one single class that is above the average is not a concern) then you might want to get your own testing anyway so that you know how gifted he is and know that the problem is not that he is being overwhelmed because of the extra work.
Wishing that he was never born and wanting to be dead are different than planning a suicide. You should be very concerned and careful, and I think you need him to have an evaluation anyway, but since most educational evaluations are done by psychologists, once you tell them of your concern, they will also screen him for depressive disorders and will do ratings scales that will identify any clinical area that needs treatment. If you are only concerned about the morose statements, one way to get a referal for educational testing is to take him to a therapist, it would probably be play therapy, but good therapists will pick up on any educatiional cause to emotional issues and refer kids for more detailed testing to aid in treatment, so you could go that route.
Your physicain should be able to refer you to psychologists, neuro-psycholgists, therapists, or developmental pediatricians in your area. You can get to the same end point with any of them, and it may depend on your physician's experience and who is in your area as to who they refer you to. If you don't need a referal, it is really your choice, but for what you are describing, I would start with a psycholgist who does educational evaluations.
If you get his GT testing and have trouble understanding what you are reading, you can PM me, I work as an educational advocate for children with special needs, and I may be able to help you understand what they mean, or at least point you in the right direction.
I hope this helps, sorry to be so long.
M.