I understand what yo are saying about trust. This used to be an issue for me, and sometimes I still have problems with it. All Christians do, as well as non-Christians. We sometimes call it the "faith" issue. Faith and trust are, indeed, the same thing.
There are many reasons that I personally trust God. They include personal experience, what He has done for others who trust Him, and things I find in the Bible for a few. The greatest, though, is His love for us. God created us, and He loves us all like a son. The Greek word used for God's love is "Agope" meaning, unconditional love. People have really changed the meaning of the word love in the past few centuries. The Greeks were smart, they had three words for love, all with different meanings.
God loves us like sons (and women like daughters). That means He doesn't care what we do or how much shame we bring to His name or to ourselves. He loves us, and will help us if we trust Him. God loves us so much that in order to create a way for us not to have to be separated from Him after death because of our sin (any offences against Him or others), He sent His only son Jesus, to die and shed His blood to pay the penalty for our sins. For three days, Jesus burned in Hell because of our sins, but on the third day He overpowered even death itself and came back to life. He then ministered for 40 days to us on Earth; and then, having fulfiled His Earthly duty, went up to Heaven to be with God. God loves us so much that He would have His own son go through all that so that we could be with Him, and He (Jesus) willingly did. You may already know this, being a former JW.
If God loves us that much, I think He can be trusted, don't you?
As for Him changing the system of morality as we know it and the concept of free will, why would He? His system of morality has everyone treated exactly fairly, if we would obey it. And free will is here because, I may have said before, God wants us to want to love Him. He doesn't want us to be like robots programmed to worship Him, he wants us to have another option, and choose Him. That is true love. It's in movies too. A guy is faced with the option of two girls. One likes him for his body and is just in it for sex. The other truly loves him because of who he is and stuff. That's a classic, very commonly used plot for love stories. The alternative is like the guy is forcibly married and there is never any real love in the relationship.
Sin wants us for the sex, but God truly loves us. It's our choice. If we chose God, then that means it is 'true love.' That's why God doesn't change morality or free will. He could if He wanted to, but He doesn't. If it's a display of power that you're looking for, read the Bible. Anywhere will do; the Bible is full of displays of God's power.
Sorry for the long message
