I have a 2 wd 2001 v 6 explorer. A few days ago when shifting it into "R"it just gave a jerk and now it is as if the automatic transmission is slipping. Forward is operating perfect. I changed the transmission filter and fluid , but to no avail. What could be the cause of the problem and what is the least expensive solution. I need this advise as I will do it myself. The vehicle has just over 80 000 miles on it , hence not excessive high milage.

 

It sounds like to me that the reverse band may have broken, we see that happen sometimes. The only way to fix it is to remove the trans and completely disassemble it to get to the band. It just happens to be the first thing you install into the case when you rebuild this trans.

You can remove the pan and the reverse servo to make sure the band is broke before you remove the trans just to be sure.

 

If you manually put it into low1 and it works and it has engine braking your band & servo is good, I have the same problem with my 2000.
Check your shifting linkage, if no luck with the low1 you might pull the pan and remove the reverse servo piston and check the tip of the piston rod for breakage also the o rings for any damage.
You can carefully put a screwdriver up the piston rod hole and feel if the band is still there.
Could be in the valve body also.
The reverse band is not adjustable except for longer piston rods.
If nothing seems to work and your pulling your hair out like me maybe look into a rebuild like I'm doing.