Without more context, it is difficult to be sure, but I think that in this sentence "speed" has its ordinary meaning of how quickly something moves. I think the passage is a long way of saying "I cannot go any faster."

"Gotta" is both slang and poor pronunciation. In saying, "got to" the two words are often slurred into one, hence, gotta. Having said that, the use of "got to" is incorrect. The correct way to word your question is to write, "Hi, everyone, I have a question..." The verbs "have" and "got "are often incorrectly used interchangeably. Among its many meanings and uses, "have" means to possess whereas "got" means to obtain. In this case, you clearly have a question for which you have obtained (gotten) two answers and a comment. As for answering your basic question, I agree with Kenneth's response. The author is being more creative and perhaps a bit glib and flippant in saying he's not going to go any faster.

Try to avoid slangy words like "gotta" - you'll see the native English speakers here don't even use them. Also, "gotta" means "got a", therefore you've technically written "got a a question"... even in slang English, it's wrong.