Alright, I need help, I am now desperate!

Ok, I am desperate guys..I need some help! My roomate has a 2000 ford explorer which is having some tranny problems. I know a lot about my mustang so he thinks I should know everything about his truck ANYWAYS, I have been out there several times in the past week looking at it. He says sometimes it will not go into reverse, it will make a metallic clanking/grinding sound instead. It is a 4.0l with a 5R55E tranny. I tried to trouble shoot with the dealership but they treated me like I was stupid ... I realize this isnt a mustang question but I know a lot of you out there have a great deal of knowlege about things other than stangs.
We car pool to school to save on gas, and I am SO tired of pushing the beast out backwards!!

Thanks a lot for the help guys!

thanks for the advice! i will try to jack it up tomorrow and look at it.. Nope, it doesnt have any problems moving forward at all.. strange i know...