13' tunnel hull motor height

[tunnelvision07]

I have been working on this boat for a while and I'm just starting to test it on the water. The other day I took the boat out after moving the gas tank to the front and lowering the motor a little. I hit 55mph pretty fast. I was driving strait and then all of the sudden the back of the boat started trying to come around. I was able to correct it but, it was definitely a scarry feeling. My question to yall, is this caused by the motor being too high or weight distrubution? or both? how high should I run my motor on a tunnel. The boat is powerd by an evinde 75hp with a 12.5x23 cleaver. Here is a pic of the inside. Let me know what other info yall need.