abs lights and brake lights

Help! I have a 2000 gmc sierra 1500. My abs light & brake lights come on and also both turn signals will come on when the accelerator is pressed. the abs & brake light comes on uselly when I hit the brakes but will come on other times. I have no other problems with truck other then it looks like a chrismas tree when I drive it. Ok thats not all the kicker is I trailered my camaro last weekend and when I hooked then trailer up the light problem went away. when I unhooked the trailer the problem came back. could it be that by hooking the trailer up the trailer it is grounding it and by unhooking it I lose the ground. I'm totaly stumped. Any help would be greatly appreciated. Also when the headlights are on and you have it in gear and give it throttle the turn signals will both come on dim. Also have noticed when you jump into it you can feel it hesitating, HELP!