Bought 96 Explorer for parts

[rasouth]

Hey guys... I just bought a '96 Explorer 4.0 V6 for parts (cat converters, exhaust, rear glass, door parts, etc...). Engine runs smooth, no known leaks or over heating problems, new alt, new radiator. Put a new battery in it and took it for a short test drive. Hard shifting and slipping. Low tranny fluid. Filled it up and idled it for a while going through the gears. Checked fluids. Forward gears seem okay. Tried reverse and felt it engage, RPMs dropped slightly but no reverse action. I gave it a little gas and it seemed as if it was still at idle, just barely coasting backward. Fluid was okay. Tried it a few more times with same results... Felt it go into gear, RPMs dropped slightly and coast back.
It's just a parts car so I don't plan on dropping a whole lot of money into it. I just wanted to know if maybe this might be an easy fix so I can sell tranny and other parts I don't need.
The guy I bought it off had tranny rebuilt less than 500 miles ago. (Showed me the receipt and paperwork on what was done to it.) It was his daily driver. He stopped driving it because it would not pass smog check.
It has been sitting around since April 2015.

 

[Macgiobuin]

Reverse servo cover in the valve body may have come loose. There are 4 screws that hold it in, and if it was rebuilt recently, one or two of them may not have been torqued right. Also, the reverse servo tightens a band; the contact point where the servo rod meets the band may have broken off the band. New band may be needed. Probably one of these 2 scenarios.

 

[rasouth]

That means pulling pan off? The last time I did that tranny fluid spilled all over garage floor. Any way of putting a drain plug into pan?

 

[Macgiobuin]

After market bolt on drain plugs are available; but you gotta take the pan off to install one. Some torque converters have a drain plug, but they don't drain what's in the pan.