transmission problem for 1999 ford ranger

I am needing help please. I have a 1999 ford ranger xlt 3.0 litre v6. It will not go into reverse or drive but will engage drive 2 and 1 with no problems. The automatic transmission oil has been changed with new filter, still no reverse or drive. no metal shavings were found in oil pan. I had no problems at all, this just started up all at once, no warning. Most everyone I have talked to say I need a new automatic transmission, but I am hoping that someone here can maybe help just in case it is not a problem that involves getting a new transmission, just maybe some parts. I thank you for any help with my problem.