Need help slash/3pm 2.4ghz

[mambarustler]

So I got a great deal on a 3pm 2.4ghz with 2 receivers and case for $140 shipped. I read the instalation instructions and everything, my problem is I don't have reverse. Am using a mm esc and a 660 sized brushed motor. I have reverse enabled on the esc but nothing and I have tried messing with a few other settings and same results. The only way I can go in reverse (really really slow reverse like 2mph) is when I set the throttle trim on the radio to -100 %. ????