3 things I need help with on my 86

[Harmon]

1986 Chevy shortbed truck.

1. I have a braking issue. When I push the brake pedal, the truck slows but hits a point when the rear tires lock up. It doesnt always do it, but I was wondering what should be my first thing to check out? (Yes there is plenty of brake fluid)

2. When Idling, the truck kind of runs rough. I just replaced the plugs and wires. There is so many vacuum tubes on top of the engine I am wondering if that could be the issue? Im not sure how I could ever know where there all supposed to go.

3. My truck cannot peel out. It is one of these Goodwrench "Hecho en Mexico" 350 motors. Just wondered if this was typical.

Thanks.