Coming from a Pentecostal/Baptist back ground myself I have had these same questions.
At this time in my life where I am studying LDS I can say that they do not teach another gospel. If a gospel is teaching the word of God and knowing what it means to live life as a Christian. I think more then anything they uphold with no fear the truths of the bible. I have found in my communities that Christianity here is tepid and wishy washy. The leaders of our churches do not seem to have uniformity in the meaning of many aspects of Christianity. If I as a mother would not want to teach my children in such an ambiguous, vague sort of way why do I accept that I can not understand Gods will for me if he is trying to show me? I have considered that when I put an argument against LDS to my mind and an answer comes back that it could be from the enemy but I have to ask myself; Why would the enemy want me to live in a way so in line with Christianity and deep morality and accountability?
He could put more effort into living a worldly life and trying to dispel all Christianity. In any case, this has just been my thoughts and experience so far. If you believe in God and you say to him "Please put the answer in my heart" I am sure he will tell you. Any father would. Hope that helps :) Take Care.