Transmission Stoped working no reverse

I have a 2002 GMC Envoy SLT 4WD, It has a 4.2 liter in line six cyl engine with approx 70,000 miles on it. The transmission is making a load whining noise in park and nutrel and reverse and some low whine noise in other gears. It will pull in drive and 3rd and low but it does nothing in reverse except make a load whine noise. The filte and fluid has been serviced about 20,000 miles back. What do you think the problem is?