First off, if it has been seven years or less since you exited high school, your records should still be in the archives (if longer, they may be there, or they may have been purged). If this applies to you, write immediately to your old school system and request all records, including your cum file, guidance records, special education records, and psychological testing. (You may not have anything in some of these categories, but then again, you may, and just not have known about it.) You have a right to any records that are there. These records may answer some of your questions about your educational history, and why you were repeatedly tested, without any apparent outcome.
I would agree with the other posters that it is worth looking into 2e. As you are concerned about how this may affect your immediate future educational and career planning, I would suggest that the simplest and most comprehensive solution would be to seek out a good psychoeducational evaluator who has worked with 2e adults. It can be a bit pricey, but it is likely to give you a great deal of insight into yourself, and factors that may affect your personal and professional interactions. Secondly, it may result in recommendations for accommodations for standardized testing or instruction. If it does, you will have to be assertive and well-informed to advocate for 504 accommodations in future graduate or professional school placements, but it could make all the difference in helping you to master your profession of choice, and demonstrate your strengths.
Your history suggests a word-level reading disability (aka dyslexia), with poor phonological processing, which is believed to be the core deficit. This is why you essentially learned to read by sight, instead of phonics, and why you report a history of being a poor speller. Incidentally, this can still be remediated, to some extent, in adulthood. If you choose to seek evaluation, it will be important to mention this to your evaluator, and to make sure that phonological processing is assessed, preferably using the more sophisticated processing tasks, such as those involving phoneme manipulation.
I wonder if you would have had more success with math reasoning, and thus progressed further in math instruction, if you had been allowed to use a calculator, so that lack of automaticity and fluency in arithmetic would not have prevented you from continuing to build math problem solving skills. It sounds like rote/basic skills in general are much weaker than your higher-level reasoning and application skills. That is very much characteristic of specific learning disability, especially at your age and apparent overall ability level.
Your sudden flourishing in college, in terms of writing, may be related to the fact that everyone uses a wordprocessor then, so those people who really need it as an accommodation (for spelling, punctuation, mechanics in general) no longer stand out in any way, and language mechanics also no longer holds them back. The absence of such accommodations on standardized testing, like the GRE, might have affected your performance, depending on how mechanics is scored.
Overall, your profile suggests that an evaluator might want to investigate what has been called right-hemisphere learning disability (overlaps with DCD, dyscalculia, can include dyslexia, often is associated with differences in social arenas).
